I warmly recommend Loft Il Prato, if you want to stay close to the city centre, but away from the tourist masses in a quiet area. The Santa Maria Novella Station is within 5 min walk, and it took about 10 mins to walk to the centre.
Elena replied my messages promptly and she made me feel very welcomed. She and her husband introduced the flat and kept in touch asking if everything was ok during my stay. The flat was as described, very neat and tidy, and it had everything we needed.
I would stay here again!