with car, stay near the outside boundary of the ZTL
Happy holidays to you and your wife! I am sure you'll have a great time in Florence for the end of the year!
With a car, I suggest staying outside of the ZTL area (limited traffic area is off limits for non-residents) so you won't run the risk of incurring any fines by driving in or out into the area that is off limits. Your option would be staying very close to the outer boundary of the historical center so that you're close enough to a large parking lot where you can leave your car....... or completely outside of the ZTL (limited traffic area) at a place that offers parking space.
Here are some properties I know would be perfect since they are in the center but close enough to the "boundary" of the ZTL that means your car wouldn't be far off.