The apartment is in the heart of Florence- 30 seconds from the Duomo, 10 minutes from Ponte Vecchio, 15 minutes to the train station. Nearby, along Borgo degli Albizi, there's a large collection of cool bars and restaurants, including a supermarket. The street felt very safe at night.
The apartment itself is on the second floor without a lift which may be a problem for someone with knee problems. It is extremely well stocked (including spare light bulbs!), clean, and quiet at night. It is quite large so plenty of room for two people. There are two double mattresses; the second one is up a narrow flight of stairs. The dryer on the washing machine was a little weak but there is a clothes airer so that works well. There is an aircon/heater that works very well. Like most old Italian apartments, there isn't much natural light. I think this is standard though. The mattresses are passable. The TV is in Italian but there's great wifi so we were able to stream anything we wanted to watch.
Elena is absolutely lovely!!! She and her husband met us at the apartment and helped us carry up our heavy bags. They also left us a bottle of wine and cookies. She replied instantly to all our queries and let us check in early and check out late. They apparently live close by but we didn't have any issues. I really think you won't find much better for any trip to Florence!