Best of luck and I'm sure you're making the right decision. What I hear from Knott is some folks and even some doctors push for a TKA too early. A patient complains of pain when hiking downhill, well everyone's knees hurt some when hiking down a mountain. Suck it up and strengthen your hams, gluteus and quads.
But if your activity is declining so much you run the risk of losing muscle strength. You're an athlete, you will do the work but you just can't move anymore. Knott says or at least my understanding is good doctors want to hit that sweet spot where it's needed but not so late that you've lost any motivation.
So keep you active and moving is the goal.