I highly recommend Marco's apartment. It's nicely renovated, spacious and very clean. The location is fantastic. It's just a few minutes walk from the Santa Maria Novella train station and about a ten-minute walk to the most of the major sites. Marco was very responsive in communications and his father, who showed us around the apartment, was helpful. The only consideration is that there is definitely some street noise outside the bedroom windows but, if you're used to city sounds, you should be fine. It was the perfect apartment for our stay in Florence.