Both the AFE - Jeremy Pratt and Trevor Thom series of manuals are excellent. It is very likely that your chosen school will use one of those.
If you have chosen the school that you will be doing your ppl with, I would go for whichever series of manuals they use? You could then get the first one in the series to give yourself a bit of a head start.
AFE - PPL1 covers all aspects of the ppl generally and would be a very good place to start. Not sure what the equivalent is for Trevor Thom? You can buy them online in such places as ebay, Transair, Flightstore etc.
You probably won't need anything on top of whichever series of manuals you go for. As Johnc21 says, MFS is helpful for specific things such as instrument layout/familiarisation etc, but generally it's not a great deal of help.
Great idea to get started early with some reading and good luck with your training!