[Batty]

See, Tiva, I can't use a balance ball because we don't have the room.

Honestly, the best way to tone your body is with your own body weight, with the help of weights and dumbbells, resistance bands, etc.

Lunges [you don't have to go all the way down, just enough that you can feel it, I have bad knees too, and I take it easy on the squats and lunges] Squats, tricep kickbacks, straigh leg deadlifts, crunches, bicycle crunches, leg lifts, [think Jane Fonda, its old school, but it works xD] mason twists [also known as trunk twists] all work.