Most of the time I use my kitchen swivel chair - it's leather and very cushiony. Sometimes I use my computer chair. I like that the height adjusts, but it isn't very cushiony and hurts after awhile. I did see one at Office Depot I'd like...but I haven't gone back for it yet.
Some people recommend a backless exam chair. I don't know how I'd do with a backless chair. They are on eBay pretty reasonable. Here's a link:
http://desc.shop.ebay.com/i.html?_nk...0.l1313&_rdc=1