Sixth Form help needed...?

Whilst some books will have lots of information in them, they may not necessarily be relevant to the course and so you may not find them useful. Your teachers will probably provide you with text books anyway. It will vary depending on the exam board(s) that your 6th Form uses for each subject - they may not all be the same.

If I were you I would ask the teachers which exam board they do for the subject and then go and buy appropriate revision guides which you will use anyway and you can also go online to look up the specification. From these 2 things you can then look at topics which you find interesting and then look for books in that respect to further your knowledge. From my experience, buying books without knowing what you are going to study can be a waste of money...

If you decide that you want to apply to university after A-Levels, it would be a good idea to have a particular book to talk about in your UCAS personal statement and explain how your studies helped you to gain an interest in that field...