I really don't think that any general book you buy is going to help, unless you've got a burning desire to get into the theory. For example, you can use the 1 in 60 rule in navigation without needing to know why it works (the sine of angles up to 45 degrees approximates to the angle in degrees x 1/60th, if your interested!).
The two main sets of PPL books explain what you need to know in sufficient detail - I favour the Jeremy Pratt books personally. Alot of rules of thumb actually derive from quite complex theory and are really irrelevant at most levels of flying (the theory that is, not the rule of thumb).
If you really are struggling then there are I think one or two people doing basic maths and physics course for pilots. This might be a better option. Don't forget that when you come to Aircraft Technical there's alot of stuff about engines, ignition and braking systems etc where background knowledge would in theory be useful. Unless you've got alot of time to spare you are better attacking each subject and highlighting weak areas which you can then cover in more detail if you need to.
Not quite the answer to the question but hopefully a little help.