Hi Amy,
I'm 5'2", and have a Sissel 55cm ABS ball. I've been using this with Cathy Smith's "Time Saver Shaper Ball Workout". Although this ball is the size recommended by the chiropractor, I find that it is a little too big for me in one or two parts of the tape. Since I'm unable to put my knees and hands on the floor at the same time, I can only do a couple of exercises in the advanced position, which isn't always comfortable for me. Mostly, though, the ball works fine. Maybe it would help to use yoga blocks or other props in the places where I need to touch the floor -- hey, you got me thinking! Thanks! M.