Making my own co sleeper mattress

[Snapdragon]

Does anyone have any good ideas of what I could use to make a nice mattress for our arm's reach (sleigh bed style) co sleeper? I am thinking cotton and or wool. Or maybe some type of foam if there were a good natural one, though I would prefer cotton or wool I think. Has anyone made a good crib sized natural mattress and what did you use?
Or can you recommend a good crib mattress to buy?

I am not sure how into the co sleeper I am now that it is set up. But I definitely don't like the mattress it came with so I would like to try to make it cozier and also adjust it to go flat with the bed instead of down.

[minkleaf]

I had the mattress custom made at a futon store. Just gave them the measurements of our cosleeper and picked from their selection of stuffings. I think I went with mostly cotton, it may have had some wool too. (This was over 6 years ago so I've forgotten now. And it's only been slept on a couple times by a baby. The cat loves it, though.)

DH made the cosleeper so I'm not sure of the dimensions anymore, but it turned out that king-size pillowcases just fit the mattress as a cover.