Fitball with feet provides more stability and has the benefits of a therapy ball: increases trunk strength, enhances coordination, balance and focus. Once you get up, the feet snap back so that the ball remains in one place. Great choice for schools concerned about balls rolling around when not in use.
The best and safest ball size can be determined by measuring from the inside shoulder to the fingertip and match that to the ball's diameter.
Blue 30 cm (12"): $23.95