hey Enja - I hear water aerobics is great! hopefully that will take the pressure off your back.
Leslie Sansonne has a lot of walking videos. It's basically just walking right in front of your tv - a little like walking in place I guess, but MUCH more of a workout! I love to walk outside or at the mall during my lunchhour, and her tapes are an even better workout bec there are a lot of arm movements and side steps and stuff. You buy her videos with a 1 mile, 2 mile, 3 mile or 4 mile walk, whatever you are up to and have the time to do.
you can see her stuff at www.walkaerobics.com
She has a 6 week program there called "The Walk Diet" that you can join at her website (for free) and you can get there by clicking on this www.walkaerobics.com/walk_diet_home.jsp
Also I just saw where she will be on QVC this Friday and you can see here there on that day.