"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."
These discs, under many names, are sold at Amazon or Target or other places where fitness equipment is sold.
"Patchsamkin are the posture rules the same as using a computer?"
Yes - good chair, sit up straight, have arms parallel to desk surface, etc.
The best thing both my back doctor and PT guru say is to get up and walk around for about 10 minutes every hour. This applies to anything where you are sitting for a time, including watching TV.