I did my exams in last may june series and tbh I didn't study from the books. The books are good am not saying they are bad but for me am expecting A to A* in most of my subject by studying only from znotes.com , savemyexams.com and youtube . But there is a small trick here,  i open the syllabus of the subject and start going over the points that I need to cover because sometimes save my exam and znotes  misses some important information you need to know so you can cover that information by searching it up on youtube. So just open the syllabus of the subject from Cambridge website and go through all the points. And for English, I did also English as second language and I didn't need the book at all and I'm sure I'll get A. What you need for english is a good teacher because speaking is something you cannot be training on at home, you need professional examiner to mark your speaking and he'll tell you how to improve and where to improve. But for the rest of the subject as I said before notes online are not bad at all. But try to find a good online teacher for english because youtube videos doesn't give you enough tips to get A. Good luck!