3u maths - im using the cambridge prelim 3u book, it looks better and is separated to diff parts in each exercise unlike my friend's ones which are pretty basic
chem - im using conquering chemistry by roland smith 3rd edition. not sure if its good but its really compact and small
i'm using jacaranda for chem/phys and cambridge for 3u math.
but really the recommendations you get in this thread won't be different to what's in the sticky and since people have different opinions you'll probably find it just as 'confusing'. Maybe you should go look at some of the books and see which one you find the best/easiest?
Physics in focus is a good supplement for your school textbook. It has all the syllabus dot points in order and it's relatively easy to understand. We use Jacaranda at school. Pretty good book!
For chemistry our school uses conquering chemistry. Good book!
Maths Extension 1 - Cambridge and Fitzpatrick
Physics - Jacaranda and Physics in Focus
Chemistry - Conquering Chemistry and either Jacaranda or Chemistry Contexts.
It's good to have a main textbook and a supplement don't just rely on one resource.
Hope this helps! And good luck with your studies!