Best website to book/organise Auschwitz museum tickets?

A group of 4 of us are going to Krakow from 8th-12th of January and, from what I read, we’d have a better chance of getting to the Auschwitz museum by booking in advance. However, I have no clue which site to use as there seems to be hundreds of different options to choose from! Any suggestions in particular? Also how easy is it to get there from Krakow? Would it be worth booking a tour with transport as well? Thanks in advance.