Today I had an appt at the ortho docs. I am always intersted in good posture pointers for sewing. I have tried to sit on my excercise ball but haven't quite adapted to it as of yet.
But, check this out! One of the receptionists at the ortho office was using one of these and loved it!
http://www.google.com/products/catal..._upl=&bav=on.2,or.r_gc.r_pw.&ion=1&biw=1440&bih=686&wrapid=tlif131433667051010&q=exercise+ball+chair&um=1&ie=UTF-8&tbm=shop&cid=4344218871290954589&sa=X&ei=qy9XTtSwD6q0sQLQ2qWFDA&ved=0CD0Q8wIwAg#