though I believe you will find more than enough to entertain you in Florence without venturing outside the region of Tuscany ...it is very possible to visit Rome. Even in just one day. You can catch the early morning Freccia Rossa/Argento or Italo a new train service (both are speedy gonzales trains) it is possible to be there by 9 am and then home again intime to catch a pizza at a Florentine Pizza Place.
I have done this several times with family and friends who really just wanted to "see" Rome. It is a packed day, and if you really want to get in to any place be sure you reserve in advance. Rome is not as "walk-able" as Florence is so be sure to wear good shoes and be prepared to dive into the Italian public transport service.