Hi thinkgod! Hmmmm, that's a little tricky because a lot of my easier to follow workouts will still have impact in them. Likewise some of my low impact workouts have trickier moves.
Right now I would have to say you would be safest with the Basic Step Body Fusion DVD. The 30 minute step workout is all low impact and has simple moves. The body fusion workout (also included on this DVD) is a little more advanced and has a bit more impact so you may want to wait before attempting that workout.
Good Luck!