I bought an DynaDisc by Exertools many years ago and use it for when am sewing not at my home. This was originally for physical therapy and balance but once I saw it I knew it would be great for classes, sew-ins, etc. What is pictured is similar.
I have a Swooper that I use at home for sewing. It is height adjustable and more; looks like a giant mushroom; is like sitting on a balance ball so my posture remains what it should be.
ali