The OCR Textbooks would be helpful. You can get them on Amazon, just search for the ISBN number.
OCR Chemistry A2 ISBN - 0435691988
OCR Biology A2 ISBN - 0435691902
They're quite well laid out and text is broken up in (what I think is) an easy to read & understand format. They're also useful for revision because of the style and as they're direct from the exam board, examiner's tips have also been included which can be quite handy.
I found CGP guides to be pretty helpful; they explain difficult topics in a way that is much easier to understand and take in. You can get them off Amazon for a decent price, even cheaper if you're a scav and get them second-hand like I did. Haa.