Fulvia is a great host and I'm very glad I got to stay with her (and with her very friendly cat, Nilo)!
Fulvia's apartment is in a great location, around twenty minutes from the Vatican and a Metro stop. It's in a nice neighborhood that is just far enough away from the main tourist attractions that the people you run into on the streets will be mostly Italians. There is a grocery store and a fruit stand just around the corner.
I just walked everywhere I went, although I understand that there are buses.