This might be really stupid, but, here goes...had a similiar problem...someone recommended two possible solutions:

1. Buy a few sets of the same size gel foot inserts (Dr. Scholl's or cheap knock offs) & some double-sided carpet tape. Use a chair-size piece of material...stick the foot inserts on to the material using the double-sided tape. Uses as a removal cushion where ever you need it. (If you can stand on those babies in your shoes, sitting on them should be just fine).

2. Sporting goods stores carry all kinds of thin cushions for boating & sitting in stadiums for sporting events.

Hope this helps!