Carol, remember that most of the people who post here are looking to solve problems and only a few people post their success stories, so you are getting a very skewed view of success rates on this website. Besides myself having both knees done, I personally know three other people with TKR's very well, and all of us are happy with the results. If you are an active healthy person before surgery, have a good surgeon, do pre-op exercises and work hard at PT afterwards, there is every reason to believe that you will have a good recovery. I am now 75, had separate knees done at 72 and 73.
As far as stairs, I live in a stupid house where the kitchen and main living area as well as our bedroom is up a full flight of stairs from the entrance. I came home from the hospital the day after surgery and had to pull myself up 13 steps using the handrail - moaning and groaning all the way, but I got it done. I had to use the stairs nearly every day to clean the cat litter box or do laundry or use the chest freezer. I believe that being forced to use the stairs speeded up my regaining flexion and knee strength. You have to push your knee to its limits in order to work it back to a good range of motion, and this should start right after surgery. And of course lots of icing and elevation of the knee.

I have no problem getting off the floor, you just have to figure out a way to twist around so that you don't put all your weight on your knees for rising, so you do need good arm strength. You won't be able to do it right after surgery, so plan to do some of your recumbent exercises in bed to start with.

I do a lot of gardening, I have a boat safety cushion that I can kneel on with one knee, putting most of the pressure below the knee cap by having the knee itself off the cushion. Walking is no problem, I can do anything that normal daily life requires. I only do occasional light yoga, cushions under the knees are a must, and I can't flatten my knees very far when sitting cross legged. I believe you are supposed to avoid movements that may twist your knee sideways. I have not been kind to my knees, I had a fall earlier this year, coming down hard with both knees on a pile of hard dead branches, and then flipping a hammock and hitting one knee on the metal support bar underneath. In both cases, I was able to walk off the pain within an hour or so and assume my artificial knees were not damaged.

TKR's will never feel like my original bone knees, I'm aware that something "else" is in there, and I have clicking in both knees most of the time. But I no longer have the dull pain of arthritis or big jolts of pain coming down stairs. I would do it again.