Other Reference books

If you are watching my free lectures (together with our free lecture notes) then you do not really need any reference books.
The lectures are a complete free course and cover everything needed to be able to pass the exam well.

The books you do need are Revision Kits from one of the ACCA approved publishers (BPP or Kaplan), because they are full of past exam questions for practice and practice is vital to passing the exam. (Revision Kits from other publishers are not as good because only BPP and Kaplan are allowed to publish past exam questions).