Thanks for the reply, Nurioopta and Sydneynick!
Nurioopta, I actually went over seat61's page and video on the Thello, as well as a few threads regarding the Thello on TripAdvisor. Seat61 states you pay by the berth (bed), so I'm 90% sure we should be booking the "Cabin 2 beds". I'm just wondering why they would allow you to book 2 in the "Cabin 1 bed". Is the 1 bed bigger that it can accommodate?
Sydneynick, our original plan was to fly direct from Paris to Florence with Vueling Airlines ($326 for 2 people, so cheaper than train). However, my husband's manager who vacations to Italy every year for a month, advise us that the Florence airport is highly unpredictable during the winter holidays, and may shut down. We would still be able to get to Florence with all the detours they make, but the original time saved may not be much, if any. Thus, the decision to take the long train ride. =(
Thanks for your time again!