I got my foam from
Foam Factory
If i remember right they are also Foam by Mail.
My foam is in 3 pieces cause of the under bed storage/foot well. I then wrapped the pieces with old sheets. Works for me.
Foam
That is what I used, 5 inch thick. It is plenty firm, I can set on it and i will not compress it to the wood and I weigh almost 300 lbs. A less firm foam would probably work for other people. 5 inches was to thick, could have gone with 3 or 4. Maybe even 2 with 2 inches of a much softer foam over that. Not memory foam in my book. I have tried that in both the TD and home and removed it. Just did not work for me.
Randy