I don't use a chair at home. I use mushroom shaped sit-upon called the Swoper. I know they sell the at Sit4Less on the 'net. It is like sitting on a balance ball and I keep my posture better with it.
When quilting somewhere else I will take my Dynadisc by Exertools. They use this in physical therapy for balance training. I know they sell it at LQS's and some quilt shows but forget what the name is when sold this way.
ali