An article in the Houston Chronicle discusses the ergonomic benefits of swapping a typical office chair for one of those fitness balls you see in the gym. The idea is that it makes sitting (which, when done day in and day out, can put a strain on your back) a more active pursuit since your muscles need to adjust continually to stay balanced on the ball. Using the ball “virtually prohibits the slouch and removes the temptation to cross your legs.”
This isn’t the first time I’ve read about using ball chairs, or just fitness balls, for sitting; believe it or not, I actually own one (even if the sitting thing doesn’t work out for you, they’re awesome for ab work). I rolled it over to the computer and gave it a try for a while, but found the one I own doesn’t quite fit (despite being rated for a person of my height, I was lower than a chair puts me, and I had to look up at my monitor). A round with my bicycle pump only improve the situation slightly. However, I bought the ball as a toy for my home gym, and I wasn’t thinking ergonomic seating. Talking to a therapist might help you find one that’s just the right fit.
Just the balls themselves aren’t too expensive. The actual ball chairs (they look like regular chairs with back rest, legs, etc., except that the seat is a ball) I’ve seen run a about a hundred dollars.