I'm using the study guides and course companion for Biology, and between them I'm getting through it. I've also got the course companion for English which is helping.
I think they're a pretty good collection. It's quite difficult to find IB study guides, so I'd recommened seeing if the Oxford study guides also have ones for your other subjects.
It might also be an idea to get a couple of A Level revision guides, but check first to see which exam boards offer similar courses in content. The way they'll test will be different of course, so just ignore all of that, but I've been using A Level revision books for philosophy and psychology, and it sometimes can really help either to just get extra info on a topic or help understand more complicated ideas.