Arthritis in my knees

I have arthritis in my neck, back and knees. The knees are the worst. An orthopedic doctor said I was a candidate for knee replacement quite a few years ago. I would have it done except I'm about 100 pounds over weight due to a necessary psych med I have to take - thank you zyprexa. I also have poor circulation in my right leg which has the most knee pain. I'm so afraid that if I have the surgery I'll end up worse than I am already. I used to love to go for walks but now I walk as little as possible. When I have to go to the grocery store to buy my groceries I take an NSAID several hours before and then take my cart since I don't have a car. That helps but because I take an SSRI antidepressant I can't take the NSAID very often. The 2 meds aren't supposed to be taken together long term. I'm only 60 and I feel so old and limited. If I'm going by bus to meet a friend for a meal I take my walker which has a seat. I swear my psych meds are saving me but they're killing me. Has anyone who is obese had successful knee replacement surgery?? I tried a cortisone shot which worked great but only for 2 weeks and I tried the series of 3 hyaluronic shots which did nothing.