I second the vote for more time in Rome than Florence. Florence is wonderful, but Rome is much bigger and fuller. You could spend the entire 5 days there and feel like you've only scratched the surface. Reserve ahead for the Uffizi, and arrive early for the Vatican Museums; the lines for both get long.

In Florence, we stayed at the Hotel Globus (http://www.hotelglobus.com/). In Rome, the Hotel Domus Tiberina (http://www.hoteldomustiberina.it/index_en.html) in Trastevere. The Domus Tiberina is simple and charming, the Globus a little posher but still not too expensive. We liked them both.