Not sure if you have Starwood points or not, but my wife and I stayed at the Grand Hotel Florence with Cash & Points, and it was US$165 a night (including taxes) and 8,000 Starpoints. We stayed 3 nights and loved the hotel. Had a river front room on the top floor that was enormous. Plus the hotel delivered a bottle of champagne to us on our first night to congratulate us on our wedding. Could not have been happier! And the location was perfect for exploring all of Florence and a short walk from the train station on top of it (making our departure quite easy). We arrived by car (Hertz) which also happened to be right around the corner as well.

Also, while you are in Florence, you must try La Giostra. By far our favorite meal in Florence and one of our favorites in all of Italy.

I would avoid Acqua al 2 (also referred to as Acqua al due). It is a blatant tourist trap IMHO and has subpar food. We regretted it so much that it was our last meal in Italy. We should have went back to La Giostra and to this day kick ourselves for not doing it.