We would like to book tickets for only the Uffizi museum; we are not purchasing the firenze card. What is the official website?
http://www.polomuseale.firenze.it/ Click on the Union Jack flag on the top right of the screen to get the English version of the website. You can also phone to reserve your tickets. The cost is the same as there is a reservation fee. There is a choice to have your call answered in English. There are generally more tickets available if you phone.
Our B & B hostess did this for us and had the tickets waiting when we arrived.
We phoned a couple of days ahead (in October) and it worked fine. I'm leery of relying on your lodging to do it for you - we are talking about Italy, reliability isn't one of their endearing features.
We also had our B&B get us reservations at the Uffizi and the Accedamia. The B&B emailed us 6 digit reservation codes for each of the museums. When we attended the museums, we showed them each our reservation codes at the designated counter and picked up and paid for our tickets. It was very easy.