I self taught A level maths (Edexcel) so I can only speak for that and not further maths.
Essentially, all you need are the standard textbooks (Pure Y1 and Y2, Stats and Mech Y1 and Y2=4 books all together) and Youtube and for me that was enough. The books have more than enough practice questions for each chapter and subsection. For further practice, there is so much stuff online and pretty much every past paper you can find online as well.
The textbook is decent but sometimes underexplains things if that makes sense. For Edexcel maths, pete hart on Youtube is the best imo, he goes through literally every chapter in the 4 textbooks. He doesn't do a lot of practice questions but explains the underlying theory/method for many chapters well. If you need help going through practice questions, there is this guy called Zeeshan Something. Just type Zeeshan A level maths and his channel will come up, he goes through the practice questions in the textbook, not all of them but enough of them imo.