I used the Collins textbook for self-study and found its explanations clear and engaging. It also contains exercises throughout and at the end of chapters. I didn't like the online textbook supplement for the optional topic as much though, so I also used videos. I don't recall specifically how closely the definitions match the specification, but savemyexams revision notes, PMT practice questions and past papers are quite helpful for this.
I think a lot of people use the CGP textbook for self-study, so you might want to look at that one as well.