One of our good buddies had it done a couple of years ago...he put it off because he wanted to continue to play volleyball, and once he had it done, the doc told him no more of that...he was in excruciating pain...finally said okay.
He had minimally invasive replacement...recovery time is much faster. He can walk normally without any pain now...so glad he did it.
The only way to lose weight is to reduce portions and get active, which I know will be somewhat difficult...but you can take hand weights and do arm work, strengthen the back and chest muscles with them, too. Eat breakfast, mainly protein. Veggies...we're doing a modified South Beach diet here, and we feel so much better nixing the carbs.
Good luck and keep us informed!