You'll get by with one textbook, but don't expect to excel at your subjects. Take physics for example, which I studied at A-Level. The CGP revision guides will cover the essentials and give you a couple of (relatively easy) practice questions, but this won't take you very far. A-Levels are about having a breadth of knowledge that you can apply to each other. If you really want to do well at your subjects, make use of other resources like textbooks (for physics, if on the OCR board, I recommend "A Level Physics for OCR" from Oxford Press) to further your understanding as best you can.
It's not enough to just know the content at A Level - you need to understand it.
I should say, I agree with others that it's certainly possible to do very well in your subjects with only one textbook. But it's going to take a hell of a lot more work. Also for physics I recommend physicsandmathstutor, do the practice questions to death - it'll only help you.