You can also put the ball between you and the wall, and lean against it. The do the squats that way. (Basically, you lean against the ball so it takes some of your weight, and helps keep your weight back, and then it rolls so you can squat smoothly.)

Other things about squats -- make sure your weight is back, so your knees are directly above your heels (never crossing in front of your toes), AND, only going down to 90 degrees is ok.

Maybe i should work out with Sheryl - she seems to have good ideas.