We really enjoyed staying at Lorenzo's apartment. It is spacious and clean; there is a good kitchen available, shower and laundry. There is also take-away pizza on the ground floor.
The apartment is located 15-20 mins walk from the city centre (actually, we never took public transport in Florence and used to walk all the time). There is a bus stop nearby.
We are recommending it to our friends and would recommend it to young couples and families with children; especially if you don't mind 20 minutes walking.