Florence is one of my most favourite places in all the world. Only drawback at this time of year would be that it might be getting crowded. You can rent self catering apartments for just a few days, and there are lovely places to eat out and markets to buy food. Everything is within walking distance - perfect for just wandering and looking. But we do always go in the winter (Feb/March), so not sure about tourist pressure in the summer.
In the UK, we've done a two night break in Oxford - lots to see and good food and shops! (I live a long way from good shops, so this is a treat for me).