You are so lucky! Your itinerary sounds amazing -- that is a trip to look forward to! Here are some of my suggestions for Paris / Rome:
Last time I was in Paris, we stayed here: Hotel Valadon Paris - between rue cler market and eiffel tower !
It was charming, relatively inexpensive, and close to the Rue Cler, which is a cute little shopping street with little bistros, fruit stands, it is close to the Invalides, Eiffel Tower, walking distance to a lot of great stuff. In the 7th Arr. It's not five-star, but it's no-frills and charming.
Another cute location is Montmartre by the Sacre Coeur, fantastic views and windy, hilly streets. I have stayed there, but have forgotten the hotel. If you don't stay here, try go at sunset for an amazing romantic view of the city.
I didn't like where we stayed in Rome the last time we were there, next time I would like to stay in Travestere, which is across the river and away from everything, but it's romantic and quiet. But if you want to stay in the midst of it all, I think the Piazza Navona area is central to everything, but you pretty much walk everywhere. The metro in Rome is not nearly as comprehensive as it is in Paris, but with so much to look at, who cares if you have to walk?
Go on tripadvisor.com to check out ratings, that is my bible when I'm planning a trip! Have fun, and if you have room in your suitcase, let me know if I can sneak in! hahaha
PS. Don't lose track of your wallet or purse in either of these cities. I have personally seen a mugging in Paris (at dusk), and someone try to pickpocket someone in Rome (in broad daylight -- it was a kid). Not to scare you b/c these places are perfectly safe, but just be aware of your surroundings and your belongings.