The Posture Ball helps to reduce or eliminate back pain and best of all, since your "active sitting" you burn more calories throughout the day and strengthen your core! The ball encourages a slight bouncing movement that keeps leg muscles busy and eases stress.  At first I was sceptical thinking, "I’m never going to last more than 30 minutes on this thing, or I might fall off", but time goes by easily and I feel great when I get up and walk away to do other things.  You can find Posture Balls (mostly referred to as Resisto Balls or Swiss Balls) at places like Target, Big 5 Sporting Goods or they can be ordered online at places like amazon.com.  Most of them will even come with a small hand-foot pump and a workout chart for a variety of exercises you can also do with them.