I'm 3 years out from TKR and like you had some post surgery goals:

1. No pain walking & sitting
2. No pain sleeping
3. No pain going up stairs
4. No pain going down stairs
5. No pain getting down on the knees

With in a year I accomplished all of the goals except #5 getting down on my knees. My problem is and still is the weird feeling the knee has when on the hard surface. I've accepted that this problem will either take much longer or never be resolved so I took a slightly different path and purchased some very expensive knee pads. They are heavy duty professional from "NoCry". I'll include the link to a group of they're products.
https://nocry.com/search