Hi Sara
It is a bit of a conundrum. If I were you I would have a chat with the Tour Manager at the first opportunity to confirm the date and time to book.
If you don't have a laptop or smartphone, the hotel may have a computer you can use. If not, I'm sure you will come across an internet cafe during the week. Bear in mind you might need a printer too - I'm not sure how the Uffizi manages its online bookings..
You can buy tickets on the official website, so keep a note of this url (or just Google it)
http://www.uffizi.firenze.it/english/musei/uffizi/
Kind regards,
Olly, your editor