When in Rome last September my DP (with two new knees) tripped and was out of action. I think he planned that ha ha. But he had been before I hadn't. Anyway I didn't let it stop me, and TBH I just walked and walked and walked. I took the metro a few times when the distance between places was too much, but generally just wandered.
I wasn't into queuing, or skipping the line or being amongst a vast throng of heaving people in the Colosseum or Vatican museum so dodged that. I did see Collosseum from outside of course and that was good enough for me. I could read and see all about the underground and so on on YouTube 😊As for Vatican, well both DP and I made it there (before his trip up), but we didn't do the tour. I'm glad we didn't, we would have been just carried along in a sea of people and that's not my idea of fun. Again I can see it all online. We went on a day the Pope had an audience, it was magnificent, awe inspiring and breathtaking, and it was Jubilee year so the place was thronged with adoring fans of Il Papa! Huge crowds in St. Peter's Square, but well managed.
TBH the highlight of my trip (it's not for everyone) was a short train journey to Ostia Antica, the most magnificent Roman site I have seen yet, and I've been to a few. So quiet, not crowded like Pompeii and just a wonderful day wandering around with the help of a very good map from the ticket office. Highly recommend.
As for Rome itself, there is so much to see that you have to narrow it down to the must sees. I made a list and devised a walking/metro route and it took me a whole day, but I saw everything I wanted to see (Colloseum and Vatican were separate). Fantastic city, and so many layers. You could visit 100 times and not see it all. Enjoy yourself.