Skip the lines tours are essential. Especially for hot spots like the Vatican or the Colosseum. They aren't too hard to find. You can google it and book them ahead of time.
When we were in Rome (never been to Paris, can't vouch for them there) my wife and I used
https://www.ceetiz.com for the Vatican/Colosseum STL tours. We were very happy with them. For the tour, everyone gets a local 2 way radio receiver and earbuds, and the tour guide has a speaker, so as long as you stay about 20 meters around her, you can hear what she's saying.
If I may suggest it, we also went on a food tour with
https://www.eatingeurope.com which was worth every penny, as we went back to every single stop on the tour (there were 11) at LEAST one more time to eat while we were there, and some places (such as the gelato place) were an every single day stop.
I can not possibly recommend enough the STL tours. We had a 9am tour at the Vatican, and by the time we got there for our tour (we were half hour early) the lines were already hundreds of people deep waiting. The Colosseum tour the lines were even longer, as it has a maximum occupancy that they are pretty strict with.