We've both had knee replacements -- and shoulder -- while we were full-timing. Steps shouldn't be any problem for you even when you come back from surgery. They'll have you walking hours after surgery and will give you some in-hospital physical therapy. Just mention that you'll have some steps and they'll work with you right away.
The important part is to put all your effort in doing the physical therapy for six weeks or for ever how long. That's the only way you'll improve greatly. It will hurt for two weeks but do it. After that you'll see a very big improvement. Don't be afraid to bend the knee. It won't break. While you're still in surgery the doc will twist and bend that new knee every which way to make sure it works as it should. Don't worry...you won't feel it. :)
You'll be so much better and pain-free than you are now. We're even playing pickleball daily and running around the court. Best of luck to you!