Hi, My son had just become a father and in preparation for the special event, he and his brother designed and built a cot. It is custom made so a regular cot mattress won’t fit it unfortunately. I’m organizing a custom made mattress. My question is: what type of foam (if using foam) is recommended? Is the firm foam mattress material used for swags etc suitable? My understanding is that providing the mattress is firm and well fitted within the cot it is suitable, is that correct, Thank you

Red Nose recommendations for a cot is that it needs to meet Mandatory Australian Standards, from Product Safety Australia (ACCC)
https://www.productsafety.gov.au/products/babies-kids/kids-furniture/household-cots
Safety Alert:
https://www.productsafety.gov.au/system/files/Safety alert — Cots.pdf

Red Nose recommendations for a safe cot mattress are:

A safe mattress is one that is the right size for the cot, is firm, clean and in good condition and is placed flat (not tilted or elevated).

Ensure the mattress complies with the size and depth recommended by the manufacturer of the cot. A baby or toddler can get stuck in gaps between a poor fitting mattress and the cot sides. This is especially dangerous if their face is trapped and covered, or their neck is restricted in any way. Make sure there is no more than a 20mm gap between the mattress and the cot sides and ends.
https://rednose.org.au/article/what-is-a-safe-mattress

Red Nose does not recommend a mattress is made from any specific fabric, but must be firm, & not of any fabric that is soft, or conforms to the shape of the baby.
A soft mattress or sleeping surface can increase the risk of sudden unexpected infant death if baby rolls over onto the tummy.