We have just spent 5 nights in Isabella's apartment and we really enjoyed the experience. The apartment is bright and airy and is a very large space for a one bedroom apartment.
It is located about a 15 minute walk to the Duomo and the Ponte Vecchio which suited us. It's close enough to the main museums and attractions but not so crowded as the city centre. Buses are only a 2 minute walk from the apartment.
Isabella is a wonderful host who offered many great suggestions for shops, restaurants, bars etc in the local area.
I have no hesitation in recommending Isabella's apartment and we would definitely stay there if we're ever in Florence again.