I have the exact same problem, my knees just can't take it. I've been doing step workouts on the floor for a couple years now. Just like you said, "You don't have to worry about tripping and you make the movements larger". Once you learned the steps you're able to make the movements more intense...
Doreen, If you know where Quality Market is on 38th & Liberty I am just a few blocks from there. McKean is not too far from here. Maybe when the weather gets better and our schedules can fit it in. I do love Cathe's workouts.
Mary:D