Florence is one of the safest cities in Italy, somI wouldn’t worry about it. 90% of pickpocketing in Florence occurs aboard public transit, but since the city center is small and walkable I doubt you will need to take any public transit at all. For the transfer from the Florence airport or train station to the hotel, just use a taxi, which are very safe. Also when you have luggage with you it is best to take a taxi because your hands aren’t totally free when you have to lug suitcases along and therefore you are a more vulnerable target. The only other occasion when you might take a bus is to go up the hill on Piazzale Michelangelo or nearby Fiesole. Just use a taxi in those instances too, although Piazzale Michelangelo is within (long and uphill) walking distance.
Another common pickpocketing time is when you sit at a side walk cafe or restaurant and you leave your phone or purse on the table. Don’t! It takes a second to a thief to walk by and grab your belongings and run away, while you are distracted people watching.
PS: I always wear a fanny pack and never had an issue. Thieves, also on buses, like to steal stuff from back pockets (so don’t keep you phone or wallet there) or from purses (so don’t keep your valuable in your purse which can be easily snatched away from your hands or sometimes they just put a hand inside while you are in a crowded bus.