I used Kayospruce for the outer cover & zips - can't remember who supplied the foam, it was several years ago. 50mm thick foam - probably on line. Other suppliers are available.
On Jissel, we had cockpit cushions about 50mm thick, but made of a very firm foam that looked like minced foam glued back together. We found them very comfortable, and, being thin, they were easy to store when not in use. Jazzcat has a softer, 10mm foam, also very comfortable, but the big cockpit needs lots of them, and storage is an issue.
My top tip is to be sure to use sprayhood-type material. We didn't, and we'll have to replace it in the not too distant future.