Hi,
Thom and Pratt are the two main text books which people use, so you're on the right track. As for which one to use, I'd normally suggest you use whichever your instructor recommends - that way, if you have any questions, your instructor will be well-placed to help you out. But that won't apply in your case if you haven't found an instructor yet.
Personally, I used the Thom books. I'd recommend them all, except for the R/T one, for which you should use CAP413 (the official publication from the CAA) instead.
The other thing you'll want to invest in is a copy of the PPL Confuser, which contains sample questions for all the exams.
I'm not sure on the wisdom of doing all the exams first... I think it would be easier to study as you go, that way you'll have practical experiences to back up your learning. But it's certainly possible to do the exams first. Many people who do their PPL in the USA do the exams first so they can concentrate all their efforts into the flying for the short period that they're in the US.
Good luck!
FFF
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