I'm in that exact same situation now. I hurt my knee almost 2 weeks ago while doing the low impact sprinters on Cardio Slam. The knee that was hurt wasn't even the weight bearing one at the time. But, after icing it over that particular weekend, taking all last week off from exercise, I'm on day 2 of the P.volve program. I'm not here to promote another trainer or program because if not for the knee problem I'd still be jumping and pumping along with Cathe. The P.volve program is basically functional movement rooted in physical therapy. They call it "Prehab". I'm doing the 21 day Butt Lift dvd and I've done standing and floor work using gliders, ankle weights and the p.ball which is a large elastic band that looks like a Boss Band with a small ball attached to it. You put it near the top of your inner thighs and do squeezes. Its too soon to say if I think I'll see any difference in my butt. But I'm just happy that I've worked my lower body without any issues for the past 2 days. With that being said, I don't want to abandon the upper body gains I've worked so hard for, so I'm doing one body part per day using ICE Muscle Meltdowns. I have a lot of options for short upper body workouts with ICE, LITE and even the 4 Day Split series. I've had all the P.volve equipment for almost 2 years, but made excuses not to use it because I wanted to lose a few more pounds before doing a workout that doesn't have a true cardio component, but because of my knee I had no other choice and I'm thankful that I can at least do something and I'm not feeling any discomfort. There are other P.volve workouts and I even have a free 3 month trial that I've yet to activate.
Also, as mentioned above, Cathe does have workouts with options for doing floor work and barre type workouts.
Back in 2007, when I had to quit running because of a knee problem (not the knee I injured during Cardio Slam), I eased back into lower body workouts, I was doing Jari Love dvd's back then and for the lunges and squats, I wouldn't use any weights and wouldn't go as deep. I'm hoping to eventually see if I'm able to do high impact stuff again because I have a ton of Cathe dvds, in fact, I'd just gotten a few new ones in the mail the day before I hurt my knee. I might reserve P.volve for recovery weeks or just to change things up. I have their slant board workout which looks like fun and I do want to try more of their workouts while I'm in this waiting period.
Hope this helps and I hope you feel better!