In short: A safe cot mattress is firm, flat and fits the cot snugly, with no gaps around the edges. Your baby’s head should sink no more than a few millimetres. Choose the right size (usually 60 × 120 or 70 × 140 cm), a breathable core and a removable, washable cover with moisture protection. Keep pillows, duvets and cot bumpers out of the cot.
Author: Eva Birsa, mum and co-founder of Evitas · Updated: 27 Sep 2026
What to look for in a cot mattress
Apart from your baby (and a fitted sheet), the mattress is the only thing that should be in the cot, so it is worth choosing carefully. International safe sleep guidance (NHS, The Lullaby Trust, American Academy of Pediatrics – AAP) agrees on a few key points:
- Firm: your baby should not sink in. The head should sink no more than a few millimetres and the surface should not dip under your baby.
- Flat: no raised or padded edges, no incline and no “nest” shape.
- Snug fit: the mattress must cover the whole base of the cot, with no gaps where an arm, leg or head could get trapped.
- Hygienic: a waterproof or moisture-protected cover that you can remove and wash.
- Nothing extra: for babies under 1, guidance advises against pillows, duvets, bumpers and soft toys in the cot. Use a baby sleeping bag instead of a blanket.
How do I check the mattress fits the cot?
Push the mattress against one side of the cot and check the gap on the opposite side and at the corners. If you can easily fit two fingers into the gap, the mattress is too small. Australian guidance (Raising Children Network) says the gap between mattress and cot side should be no more than 20 mm; The Lullaby Trust recommends no gaps at all.
For travel cots, only use the mattress supplied with or designed for that specific model. Never add a second mattress or extra padding on top.
Cot mattress sizes
| Type of cot | Typical mattress size | Note |
|---|---|---|
| Standard cot | 60 × 120 cm | the most common size |
| Cot bed / larger cot | 70 × 140 cm | more space, lasts longer |
| Leander Classic™ cot (70 × 120 cm) | oval 66 × 116 cm | oval shape – needs its dedicated mattress |
| Cribs, Moses baskets, prams | various (e.g. 70 × 37, 78 × 36 cm) | always match the specific product |
Cot size always means the internal size of the base. Measure the base or check the cot manufacturer’s instructions before buying. For oval and designer cots, choose a mattress from the same brand.
Materials: foam, coir, latex
- Foam (cold foam or PU foam): light, affordable, even support. Quality mattresses have air channels for better airflow. Example: Träumeland North Star 60 × 120 with a removable, washable cotton cover.
- Natural fibres (coir, latex, wool): coconut fibre (coir) is firm and breathable, latex is more elastic. Example: Leander Natural 66 × 116 – the manufacturer recommends the firmer coir side for younger babies and the latex side for older children.
- Two-sided mattresses (“baby” and “junior” side): one side is designed for babies, the other for toddlers. Example: Leander Classic™ Comfort with a cold-foam core, air channels and a moisture-protected cover, tested to the European standard EN 16890.
Whatever the material: use the firmer side for babies and do not add soft toppers.
EN 16890 standard and second-hand mattresses
EN 16890 is the European safety standard for mattresses for cots, travel cots and cribs. Look for it on the packaging or in the product description. The Lullaby Trust points out that the standard does not cover SIDS risk, so safe sleep rules matter just as much as a good mattress.
If you use a second-hand mattress, it should be firm and flat (no sagging), with no rips or water damage, a well-fitting cover and no gaps around the edges.
Safe sleep in the cot
- Put your baby down on their back, feet to the foot of the cot.
- Use only a well-fitting fitted sheet on the mattress.
- Use a sleeping bag of the right warmth instead of a blanket – see our TOG chart by room temperature.
- The recommended room temperature is 16–20 °C (NHS).
Cot mattresses and cots at Evitas
In our cot mattresses category you will find Träumeland and Leander mattresses in standard sizes and for cribs. Still choosing a cot? Browse cots and cribs – for example the Leander Classic™ Baby-Junior, which with its matching mattress can be used from birth to around age 7.
Read also: Jollein baby sleeping bags – safe and comfortable sleep for your baby.
Read also: Baby Cot Guide: How to Choose (Sizes, Safety, Cot Beds) – bar spacing, side height and bedside cribs.
Frequently asked questions
How firm should a cot mattress be?
Firm. With your baby lying on it, the surface should not visibly dip and the head should sink no more than a few millimetres. A mattress that is too soft increases the risk of your baby’s face sinking into it.
Which size is right: 60 × 120 or 70 × 140?
The one that matches the internal size of your cot base. Both are standard; 70 × 140 cm is bigger and lasts longer.
Can my baby sleep on a pillow?
No. The NHS, The Lullaby Trust and the AAP advise against pillows in the cot for babies under 1, as they increase the risk of SIDS and suffocation.
When should I replace a cot mattress?
When it is no longer flat and firm (dips, sagging edges) or is damaged. For each new baby a mattress in perfect condition is recommended.
Do I need a mattress protector?
A waterproof or moisture-protected cover is recommended. A protector should be thin and fit tightly so it does not create a soft layer or wrinkles.
Sources
- NHS – Sudden infant death syndrome (SIDS)
- The Lullaby Trust – Baby mattresses and bedding
- AAP / HealthyChildren.org – A Parent's Guide to Safe Sleep
- Raising Children Network – Safe cots, portacots and mattresses
This content is for information only and does not replace advice from your GP, health visitor or paediatrician.
