Hi Karen! Try lowering your step height. If that doesn't work, you can even go so far as to put a rectangular shaped towel down on the floor (matching the shape of your step), and do the routine right on the floor.
You can also reduce the amount of power you put into many of the workouts. For example, a power 7 can simply be the same motion minus the jumping action. So it looks more like a sequential leg extension. A "basic right hop turn to the back/basic left hop turn to the front" can be a "basic right and a step knee/basic left and a step knee".
If at all interested, I also have a BASIC STEP/BODY FUSION DVD that will provide one 30 minute solid low impact step routine, as well as a 45 min. moderate impact step routine. There are weight training routines on these workouts as well.
Hope this helps!