Need low-impact exercise

Stargazer37

Hi, I have severe arthritis in my right knee, it is always swollen, it always hurts, it crunches, grinds and pops and needs to be replaced but doc won't do it due to my age (39). I had a total hip replacement in 2010 (appearantly fake hips last longer than fake knees) and have not really had any issues with it. I need to know some tips/suggestions for very low impact exercise that will not aggravate my knee any further. Thanks in advance.