HI - I traveled on this ship 5 years ago and used the following company for transportation to and from Florence. They were prompt, were able to get us to the front of the line at the museums (we had prepaid our entrance fees), and made sure we made it back to the ship in plenty of time. Wouldn't hesitate to use them again.
In Naples, I used the below company. I actually learned about them when I was in Barcelona, did some quick googling, and decided to book the trip for when we arrived in Naples. Excellent service, no issues with getting back to the ship with plenty of time to spare.
Food tip: eat the gelato everywhere in Italy. All of it. You won't be sorry.