I can highly recommend this beautiful, modern, bright flat with high ceilings. It has been tastefully refurbished and it is very well equipped. The flat was very clean and also very quiet despite its central location. The location is perfect, you can walk easily to all the sights yet you are not in the centre of the tourist crowds. If you like to cook there is a small but well stocked supermarket not too far away (Conad) and you also find bakeries, butchers and small food shops within two blocks. On Piazza Santo Spirito there is a small veg and fruit market from Monday to Saturday morning. Only a few stalls (in front of the church) but very fresh produce (maybe in summer there are more stalls but for december the choice was very good). And there are many great restaurants very close, too.
Gianni is the perfect host, always helpful, replying very quickly to any questions or request. If you plan to go to Florence this is the place to stay. I love this side of the Arno as Florentines still live and work here.