My DS who sits behind a computer the whole day swears by those yoga balls. Nearly all ladies in his office use them instead of an office chair and some of the guys. I can see a difference in his core.

Anna, I don't think I can operate a sewing machine on a yoga ball. I also roll back and forth between my embroidery machine and/or serger throughout the day. I would fall off and break something. "I've fallen and I can't get up!!!"

Costco sells a gel cushion -- they are usually very reasonable on price with good quality products.