Government and Politics required textbooks?

I'm self-studying Government and Politics A-Level in a year. My plan is to complete half the AS, then do the A2 and finally return to the second part of the AS. I'm also doing A2 Philosophy, so I reckon this year will be a challenge, so I want to be as organised as possible. Last year, when studying AS Philosophy, I didn't find out about the Lacewing textbooks (which were 100% better than the AQA 'recommend' textbook) and had to spend half of what should have been revision time getting to grips with some of the more complicated ideas when I should have just been revising. Anyway, I'm taking the following modules: Unit 1: People and Politics, Unit 2: Governing the UK; Unit 3 is Representative process in the USA and Unit 4 Governing the US.

The only prescribed textbooks as far as I know are:

Edexcel Government and Politics for AS by Neil McNaughton (covers Unit 1 and 2)
American Politics and Society by David McKay

The latter has some less-than-glowing reviews. Basically, just wondering if there are any textbooks for AS and A2 that Politics students would recommend as superior to the prescribed ones - or as supplementary readings that may help. I'm keen to only stick to around two reading sources for AS and A2 - I don't want to end up drowning in information. But equally I'd like to do my reading as I go along this time, rather than as last-minute stressful cramming.

So, if you have any recommendations for either of the courses please let me know. Would be very grateful as it's sometimes hard to know where to start when self-teaching!