I recently bought a 64 cm balance ball for work. I find that sitting all day, my posture really suffers. Now, when I am not with clients, I sit on the ball, which forces me to sit up straight. When clients are around, the ball fits neatly under my desk. On day two of this new strategy and I already notice a difference, not only in posture, but in energy.
...but the problem is, I really don't have the space to store it. Everyone I know who has one of those balance balls ends up having it rolling around in the living room or bedroom and it's just...in the way. But I do know they are good for posture and many other things. Have you tried one of those new balance ball chairs they now have available?