Definitely recommend you do book guided tours ahead of time, just because this also gives you time to better plan your days while here. You might want to do a museum per day to not get too tired of them
Here's the guided tours of the museums we recommend - guided tours of Florence's Uffizi and Accademia.
You could do the Uffizi one day, the Accademia the other. Spend the rest of the time exploring the city and enjoying the views of Florence - the whole city is amazing and an outdoor museum on its own.
Hope you enjoy your stay in Florence and for anything else, feel free to ask away!