I warmly recommend Giulia's place. It is not in the center of Florence but you can still easily reach it by walking. So you can spend your day in crazy crowds in the center, but at the end of the day, if you want to seat on a beautiful balcony, in peace and quiet, overlooking the dome, this is the perfect place. Giulia is a very kind host, she answers quickly, and she made me feel very welcome. Everything was spotlessly clean.