Exercise and loosing weight with a total Hip replacement?

Ten years ago , when I was 19 I had a total hip replacement due to an injury I had horseback riding. Since then I have had two kids and my metabolism seems to be slowing down. The more weight I gain the harder it is on my joint so I want to be sure I don't gain alot. Lately its been getting harder (I'm trying to stay around 125 lbs) but I don't know of alot of exercises that are good with total hip replacements to get lean muscle a boost my metabolism. I've tryed yoga for the low impact but alot of the stands really irritate the joint. What can I do that is low impact but gret for lean muscle gain and weight loss??

I've had both of my hips replaced.
You should be able to do these activities (provided that your physician approves):
bicycling, including stationary bikes
elliptical trainer (this is really a good workout & low-impact)
walking (ask if it's ok to use a treadmill since walking on a treadmill is slightly different than walking without one)
recumbent cycles or steppers
Some "hippies" go back to doubles tennis but personally I refuse to engage in this activity because it would involve running, which I do not do in the interest of preserving my joint.
You should also be able to use free weights for upper body strength. I also used a weight machine at the gym for my legs.
And you can always resurrect the physical therapy routines that you (I assume) had following your hip replacement. Even though I'm 5 years out from surgery, I still do some of those routines.
I walk about 2 miles 5-6 times a week at a speed of 3 mph.
You were very young to have hip replacement so no matter what you do (and if you live long enough), you'll probably need at least one or two revision surgeries.