EI
Are you looking at supplementary reading because you are struggling or because your own notes are lacking?
Only reason I ask is that you may be just as well served getting another schools notes and feedback for whichever subject it is, or indeed just buying a pile of feedback for them all.
If it's due to poor notes I would get on to your school, especially if others agree with you. I feel quite strongly that having bought a course, you are entitled to be able to rely solely on that to get through the exams, and not fork out even more on additional reading. I have some mates who had laughable notes from the old FTC and they really struggled, but when they bought oxford/bristol notes they all got on fine - though they weren't happy at having to fork out.
Obviously if it's just more knowledge you're after ignore me!!
SK