I've abandoned my office chair for a yoga
ball. The hope is that I might get a little ab-action, while sitting around on the computer. For the most part, it's very comfortable, and it encourages better posture, which I could definitely use. Still, I find that over time I start to lose my balance and the ball becomes an awkward seat.
It looks like this balance chair
might be just the right compromise for me. Essentially, it's working on the same principle, but designed to give you added balance when you need it. The best feature of all is that you can easily build one yourself.
Along with the recycled seat and back from an old office chair, you'll need 45x45mm wood x 2m and 45x65mm wood x 1m, wooden shims and a hinge. You could have rolling casters on the feet if you want to pivot and move around the office easily. Check out the full assembly instructions
, and images to guide you through the simple construction process. The end results aren't widely adjustable, but as long as you're not sharing the seat with your entire household, it should work just fine.