Cristina's apartment is everything we wanted for our stay in Firenze. It's really comfortable and super clean, and Cristina was not only inviting but also extremely helpful. Comunication was perfect.
The location is great because the apartment is around 300 meters away from Piazza della Signoria (that's in the middle of everything) but also very close to the main train station Santa Maria Novella, considering we went to Cinque Terre, Venezia and Roma from there.
I strongly advise you to rent Cristina's apartment, not only because she was super friendly, but also because it's a perfect place.