Would I be right to assume that you are already at C1 level and have already used lots of different ways of studying, and lots of different materials, in the past? If so, then if I were you I think I would start by trying to identify my strengths and weaknesses, rather than start by looking for suggested materials. That way one can take control of one's own learning. Then, if say for example my strength was my grammar skills then I wouldn't need to waste time (and money) on grammar materials, whereas if say my listening skills were weak I could focus on this area. Secondly, I think I would ask myself how I will use the language in future. I feel that some of the materials at advanced level have a potential weakness in that they assume that everyone wants to learn 'native' English, but bearing in mind that international English is not the same as the various native versions that are spoken around the world I'm not sure that is what every advanced learner wants. Would I spend a lot of time focusing on phrasal verbs if I knew that 99% of the time I would be speaking to other non-native speakers? Probably not. Would I spend a lot of time learning a lot of British expressions if I was planning on living in Australia? No

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Hey! Have you ever heard about the application which name is anki?

Hello! I recommend to see content that is aimed at native speakers (films, music, Youtube channels that deal with topics you like...) and to pass as much time as possible listening to English and watching content, trying to create an environment of immersion in your own house. As the other teacher said, the Cambridge English books are good preparation for the test since they deal with all of the skills you need to control in order to pass the text. In order to gain fluency and perfect your pronunciation, I recommend reading out loud and having conversation lessons with teachers on Italki or in person! If you're going to do a C2 exam, it is extremely important that you can prove that you are completely fluent and speak about any sort of topic using very rich vocabulary and providing well-built arguments. I hope my response was helpful!

I think any of the Cambridge English books are usually a good place to start