Last chair I bought, I went to four different stores and checked for comfort and adjust ability - then went back again to two stores to double check. I with I could afford the Herman Miller - in the meantime.. Geeze, I spend more time in my chair then I do my car, and my car cost a lot more.. I digress -
I think having one of those tilted foot thingy's helps some, but when you are kind of skinny I think it is worse on your ass and legs than if you have some extra baggage.. just a thought, I am not a scientist running studies..
I can't remember where I had originally found the air cushion site - but this will give you an idea of some keywords to search for:
Google shopping results chair air cushion circulating alternating