Please, please do not think about having both knees done at the same time.
Pain post op can vary considerably. I was in a lot of pain a month post-op, whereas a friend was able to negotiate stairs very easily a few days post op.
To start with, you do not have a leg to stand on, so washing, dressing and doing basic things would be difficult. You would need good, reliable help at home because you would have mega problems making a cup of tea. At the very least, you would be using a pair of crutches.
I have had both knees replaced, but at different times. This is my ex-professional knowledge emerging. I could go on, but you get the idea.