How to Choose a Cot Mattress: Size, Safety and Comfort

Quick answer

Choose a cot mattress by fit first: match the mattress to your cot's internal dimensions and check there is no gap wider than two fingers between mattress and frame. Then decide on construction and materials. For a standard cot, a 120 x 60 cot mattress with a sprung core and anti-allergy protection, such as the Mother&Baby Rose Gold Anti-Allergy Sprung Cot Mattress, covers firmness, airflow and easier cleaning in one purchase.

Measure the cot before you look at mattresses

Cot mattress sizes are not universal, so measure the internal length and width of your cot frame rather than trusting the label on the box. A 120 x 60cm mattress is one of the most common sizes for standard cots, but imported or older cots can differ by a centimetre or two, and that is enough to create a dangerous gap. Take the measurement at the base of the cot, where the mattress actually sits, and write it down before you shop.

• Measure internal length and width at the base, not the top rail.
• Check the mattress depth against your cot's minimum and maximum mattress height markings.
• If your cot has an adjustable base, confirm the mattress still fits in every position.

The two-finger fit test and why gaps matter

Once the mattress is in place, press down on each corner and run your hand around the perimeter. If you can fit more than two fingers between the mattress edge and the cot side, the mattress is too small. A mattress that shifts or leaves gaps can let a baby's limb or head become trapped, and it also undermines the firm, flat sleep surface that safer sleep guidance relies on. A correctly sized mattress should need a gentle push to settle into the cot and should not slide when you press the corners.

Sprung, foam or pocket spring: match the core to your routine

Sprung cot mattresses use metal springs inside the core, which can give a firmer, more breathable feel and hold their shape well over months of use. Foam cores are lighter and often cheaper, but they can soften faster and trap more heat. If you want a mattress that stays supportive through the toddler years and is easier to air, a sprung cot mattress is usually the better long-term buy. Whichever core you pick, the sleep surface should feel firm rather than cushioned, because a soft surface is a safety risk for babies.

Anti-allergy and fibre choices for a fresher sleep space

Anti-allergy cot mattress treatments are aimed at reducing dust mites and the allergens that build up in bedding over time. Look for a mattress that combines a breathable fibre cover with a recognised anti-allergy finish, and check whether the cover is removable and washable. A removable, washable cover is the practical detail that keeps the mattress fresh between deeper cleans. If your baby has diagnosed allergies or eczema, treat the mattress as one part of the plan and speak to your health visitor or GP about the full sleep environment.

Budget, lifespan and when to replace

A cot mattress is used intensively for around two years, so cost per night matters more than the sticker price. Cheaper foam mattresses can be fine for a short-term travel cot, but for a main cot, spending a little more on a sprung, washable, anti-allergy model often works out better value than replacing a sagging mattress partway through. Replace the mattress if it develops a dip, loses its shape, or the cover is torn and no longer washable, and always use a mattress that is specific to the cot it was bought for.

Decision rules for cot mattress buyers

• Fit rule: Measure your cot's internal base dimensions and buy the mattress that matches them exactly. If you cannot measure, choose a 120 x 60 cot mattress only if your cot is a standard size. No gap wider than two fingers. If there is a gap, return the mattress.
• Firmness rule: Press the centre and edges of the mattress with your palm. It should feel firm and spring back, not sink or stay compressed. A firm, flat surface is the safety baseline for every night.
• Material rule: Choose a sprung core if you want longer-lasting support and better airflow. Choose a breathable, washable cover if allergies or easy cleaning are your priority. Sprung plus anti-allergy is the combination that covers both.
• Replacement rule: Replace the mattress if it sags, the cover tears, or you cannot clean it properly. Do not pass a used mattress between children unless it is still firm and fully washable. A two-year mattress that stays firm is cheaper than two soft ones.

Products that fit this buying guide

• Mother&Baby Rose Gold Anti-Allergy Sprung Cot Mattress 120 x 60cm: Uses TENCELTM fibres with Purotex anti-allergy protection to create a fresher, cleaner sleep environment. Useful if you want a sprung cot mattress with an anti-allergy finish and a breathable fibre cover for a 120 x 60cm cot.
• Doona Liki Trike S1 - Slate Green: Folds and unfolds at the click of a button into a patented compact size that fits a car boot or an airplane overhead bin. A practical travel trike for families who need to store baby gear compactly, though it is not a mattress and does not affect cot fit.

Who this cot mattress advice suits

Best for

• Parents buying a mattress for a standard 120 x 60cm cot
• Families who want a sprung, anti-allergy cot mattress for a main cot
• Anyone replacing a sagging or unwashed mattress before a new baby arrives

Not for

• Travel cot owners who need a specific travel cot mattress size
• Parents looking for a mattress for a bedside crib or Moses basket
• Shoppers who need a custom non-standard cot size without measuring first