Good luck, Pax.
FWIW, when my mom had both knees done a few years ago, her ortho told her that it's better to have the TKA before you're completely immobilized. What he said is that people wait until they've become way deconditioned, which makes the rehab much harder and much less effective.
The surgery was hard on her, but she made a fast return and never regretted it for a minute.