Hi Meg, Annie, and Aqua!
Thanks for getting back to me on this!
My ball is a green Gaiam one (65cm.) I'm 5'6", so I bought the one for my height.
I pumped it up some more, and it IS better.
I'm glad to know that the hand pump probably won't cause it to burst.
My legs are at a 90 degree angle now since I added more air, but the ball STILL squishes a lot more than the Instructor's exercise balls do. I'm 207 pounds, though, and the Instructors probably are a hundred pounds LESS than that!
I wonder how many calories INFLATING AN EXERCISE BALL with a hand pump would burn! I have gotten quite a good workout!
Thanks to all!