Spend a few minutes, or even a hour or more, using your exercise ball in place of a chair or sofa. You use more muscles! I really enjoy doing this. I use an exercise ball (Swiss ball) while sitting at work, and at home, I'll deliberately pull the ball and use it to sit!
Try 5 to 20 minutes and see whether this "agrees" with your body. I do this all day at work, by choice! : )