When I was in very rough shape for a couple of years due to an unavoidable health crisis, I'd just do small stuff. If I could roll outta bed and knock out a few push ups, that's what I did. By the end of the day, I'd have a nice little total to be happy about. Of course, only you can judge - I get it. I really do.
In any event, hang in there. Good luck with your surgery! Let us know how it turns out! Sending up a prayer for ya!