where can I get non-toxic foam for big cotbed bumpers?

[MareMeva]

My son regularly smacks his head on the solid wooden ends of his cotbed, either in his sleep (sleep-crawling) or when falling over while standing up half asleep. He doesn't seem to mind, but I do. I want to cover each end with a block of foam, but all I have found is sold for use in seating and is of dubious composition. I know polyurethane and polyester foam and the fire-retardants often used on them can release noxious fumes but I don't know where to go to find non-toxic foam. I did fold an old duvet in half and drape it over the cot. I tried smacking my head against it a few times and came to the conclusion that it wasn't cushioned enough. Ouch. The things we do for our children. Any ideas?

Loving the idea of you bumping your head on purpose.

The only thought that came to mind would be to buy a reasonably priced cot mattress and cut it to suit but I have no idea how, sorry.

Thanks for the suggestion, Bearandcub. I had thought of that, but the Mothercare ones for example are foam sealed in a waterproof cover, but I would have to cut this cover, and they don't tell you what the foam inside is made of. I have contacted them with this query and they are meant to be getting back to me.