I warmly recommend Daniele's place. It's cosy, beautifully renovated, spotless and very comfortable. I spent a month there and I cannot think of anything that went wrong. The living room offers everything you'll need, the bedroom is very dark and quiet at night, and the bed is very comfortable. Bathroom is spacious and well-equipped.
The flat itself is beautifully situated, on the left bank of the Arno, which has some wonders to offer. It takes a 10-min walk to get to the other side where the most famous attractions can be found.
Daniele is very nice and welcoming, very responsive (I never had to wait more than 5 minutes for an answer) and he gave me some valuable advice. Arrival and departure were greatly facilitated thanks to his helpful attitude. If I come back to Florence (and I very much hope so) I will definitely stay there again.