I'm looking for good Y7 maths and English course books, to keep my son up to UK standard as we live abroad. They need to have full explanations, not just questions for revision, as I will be going through the books with him and I'm not a trained teacher. I have come across books by Letts, CGP and Collins but without buying them, it's difficult to know which one is the most comprehensive. Is there a particular book that you recommend?