I also think that your stair issues should get better in time. 4 months after TKR I still have some pain and stiffness issues, but surprisingly, the stairs are pretty easy. Considering that I had an arthro knee surgery 10/17 and never, ever, got to the point where I could walk down stairs (or moderately steep inclines) AT ALL, even after 10 months, I think you will succeed. For me, ergo, new knee. With it’s own challenges.