I can highly recommend the Maison de Charme. It is located just near the Santa Maria Novella train station. You can read more about it at their website.
http://maisoncharme.hotelinfirenze.com/ I stayed there with my wife last May and it cost about 90 Euro a night for a double room. It is more of a pensione or boutique hotel in that they have very few rooms, I think only 6 or 8. It is located on the top floor of a building, but once inside the place, it feels like a hotel, even though the establishment is small. The room we had came with a balcony that offered a nice view. I don't think all of the rooms have balconies, so you may want to request one. Our room was airconditioned, had a small fridge, and they provided a small continental breakfast in the morning, in room. The location is great, and even though it is very close to the train station, noise was not an issue. I'd go back to this place in a heartbeat. It was a tremendous deal. Don't expect the Ritz, but it is a solid 3 star property. You will get a decent sized clean room with private bath. I hope this helps. Have a great trip.