Almost every instinct you have about buying a mattress is wrong when you're buying one for an infant. Softer is not kinder. Cosier is not better. The plush little mattress that looks inviting in a shop is the one to walk away from.
Infant sleep surfaces follow a different set of rules, and they are not really about comfort at all. This covers what those rules are, how to check the fit, and how to size a cot mattress for Indonesian cots.
The Short Answer
A cot mattress should be firm, flat, and a snug fit for the cot. Nothing soft, nothing contouring, nothing that leaves a gap at the edges.
That is the opposite of adult mattress advice, and the reason is straightforward: an infant who cannot yet lift or turn their own head reliably needs a surface that does not conform around their face. A soft surface, or a gap at the side of the cot, creates exactly the situation to avoid.
Established infant sleep guidance from paediatric bodies is consistent on this. If anything here conflicts with what your paediatrician or midwife has told you about your particular baby, follow them rather than us.
"For an adult mattress, contouring is the feature you pay for. For an infant, it is the thing you are avoiding."
The Four Things That Actually Matter
Firmness
Press your hand flat into the centre of the mattress and let go. It should spring back immediately and leave no impression. If your hand leaves a visible dent, or the surface moulds around it, it is too soft for an infant.
A firm surface keeps a baby's head and face clear of the material and distributes weight evenly. It also supports the spine during a period of rapid skeletal development — a soft surface lets the heaviest part, the head, sink lower than the rest.
Fit
The mattress must fill the cot base with no meaningful gap at any edge. The standard check is the two-finger test: if you can fit more than two fingers between the mattress and the cot frame at any point, the mattress is too small.
Measure the inside of the cot base — length, width and depth — before ordering. Cot dimensions vary, and "standard" means different things between manufacturers.
Breathability and Hygiene
Babies sweat, and nappies leak. In a room running at 80% humidity, moisture that gets into a cot mattress core does not dry out on its own — it stays, and eventually you can smell it.
Two things matter here: a core that lets air move through it rather than sealing moisture in, and a cover you can actually remove and wash. Open-cell latex handles the first; a removable Tencel cover handles the second. The same reasoning applies to adult mattresses — see preventing mould on a mattress in Bali.
Materials and Certification
A baby spends more hours on this surface than an adult spends on theirs — often fourteen to seventeen hours a day in the newborn months. What the material is, and what it off-gasses, is a fair question to ask.
Natural latex resists dust mites and mould without added treatments and off-gasses less than cheaper synthetic foams. Ask any seller which material the core actually is, whether it is natural or synthetic, and what it is certified to. Our guide to what a latex mattress is covers the distinction.
What Belongs in the Cot
This is where a lot of well-meaning nursery shopping goes wrong. The safest cot is a nearly empty one.
In the cot
- A firm, well-fitting mattress
- One fitted sheet
- A breathable protector, if used
- A sleep sack instead of blankets
Not in the cot
- Pillows of any kind
- Loose blankets or quilts
- Cot bumpers
- Soft toys
- Sleep positioners or wedges
- Extra padding under the sheet
Bumpers in particular still get sold widely and photograph beautifully. Current paediatric guidance advises against them. If the cot slats meet safety spacing standards, bumpers are solving a problem that does not exist while adding soft material around a baby's head.
The same goes for pillows. Infants do not need one, and one should not be in the cot. That advice reverses later in childhood — by the toddler years a low pillow becomes appropriate — but not in the cot stage.
Heat, Humidity and Overheating
Worth its own section here specifically because of the climate.
Overheating is a recognised risk factor in infant sleep, and Bali makes it easier to get wrong. Guidance generally points to keeping the room at a comfortable temperature rather than a cold one, dressing a baby in one more thin layer than an adult would find comfortable, and checking the back of the neck or chest rather than hands and feet to judge whether they're too warm.
A breathable mattress helps at the margin, but ventilation does more. Keep air moving in the room rather than relying on a very cold AC setting — the same principle covered in why sleeping in Bali feels so hot.
Sizes and Prices
Indonesian cots most commonly take a 120 × 60 or 120 × 70 mattress, with larger cots at 140 × 70. Measure your cot base rather than assuming.
| Size | Thickness | Price |
|---|---|---|
| 120 × 70 cm | 10 cm | Rp 6.060.000 |
| 140 × 70 cm | 10 cm | Rp 7.070.000 |
Lazy Lowie Baby Cot Mattress. Prices in IDR, inclusive of VAT, 2026.
Ten centimetres is the right depth range for a cot. Thicker is not better here — a deep mattress raises the sleep surface closer to the top rail, which matters once a baby can pull themselves up.
When to Move On From It
A cot mattress leaves service earlier than an adult one, and usually for different reasons: the child outgrows the cot, or the mattress has absorbed enough over two or three years of nappies that replacing it is simply the sensible call.
Check it the same way you'd check any mattress — firmness that has softened noticeably, any visible dip, any musty smell in the core. On hygiene grounds, a cot mattress is one item worth being conservative about rather than passing down. The general checks are in signs it's time to replace a mattress.
Once your child is in a bed rather than a cot, the rules relax and normal sleep guidance applies. Why that sleep matters so much at this stage is covered in why sleep is so important for children.
Frequently Asked Questions
How firm should a baby cot mattress be?
Firm enough that pressing your hand into it leaves no impression and it springs straight back. If it moulds around your hand at all, it is too soft for infant use. This is the one mattress where firmer is genuinely the correct answer.
How do I know the mattress fits the cot properly?
Push the mattress to one side and try to fit two fingers into the gap at the opposite edge. If more than two fingers fit at any point around the perimeter, the mattress is too small for that cot.
Can a baby use a pillow in the cot?
No. Paediatric guidance is that infants should sleep on a bare firm surface with no pillow, no loose bedding and no soft objects. A low pillow becomes appropriate later in childhood, once out of the cot.
Is a waterproof cover a good idea?
A breathable protector is better than a fully sealed waterproof layer. Sealed covers keep liquid out but also trap humidity against the core, which in this climate creates a different problem. A removable washable cover is the more useful feature.
Can I reuse a cot mattress for a second child?
It depends on its condition, and it is worth being conservative. Check for softening, any dip, and any smell in the core. Given how much a mattress absorbs over two or three years of nappy use, many parents choose to replace rather than reuse.
Firm Support, Breathable Core, Washable Cover
10 cm of natural latex with a removable Tencel cover, in two cot sizes — built firm on purpose, and built for a humid climate.
See the Baby Cot Mattress →Firm, Snug, Bare
Three words cover almost all of it. Firm enough to leave no impression, snug enough that two fingers won't fit at the edge, and bare apart from a fitted sheet.
Everything that makes an adult mattress appealing — softness, contouring, padding, a cosy layered look — is what you are deliberately leaving out here.
Measure the cot before you order, and check anything you're unsure about with your paediatrician or midwife rather than a shop.