One thing I thought of--you could look into Curves or something like that. It's resistance training that is as hard as you make it, and very easy on the joints. They also promote a low carb diet (it's pretty much Atkins, though they've tweaked it a bit and call it the Curves diet.) I did it for a while, though I've started goint to the local gym with my fiance since we got a membership for christmas from my parents.