You will inevitably lose quite a bit of money in the exchange of your currency to Euro directly in Florence. We do not advise bringing your home currency for exchange as a primary means of financial support while abroad. Although there are exchange offices all over Florence, they charge a hefty commission in addition to the daily exchange rate.
A more economically convenient option is directly withdrawing from an ATM. While you will be charged an international usage fee, generally between 3-5%, ATMs (“Bancomat” in Italian) base their exchange rate off of the current market value making them a preferable method of retrieving Euro.
If you prefer to have some Euro before starting your travels, you may also order Euro from your home bank before departing.