So i've been studying theory online for about a year now and i've managed to learn a few things but now i'm sort of looking to progress to the next level.

I have a couple of books, except one is too easy and doesn't have much in there that I don't already know, and one is way too hard and might as well be in Chinese (easy - Music Theory for Dummies, hard - Harper Collins College Outline Music Theory).

Can anyone recommend a book that's in the middle?

I can read a treble and bass clef and rewrite melodies for them both.
I know intervals and where they are on the fretboard and which ones create tension/resolution.
I know the melodic minor/harmonic minor scales.
I can build major/minor/dim/major, minor, dominant 7/9th/augmented chords.
I know the circle of 5ths.
I can recognise key signatures.
I understand time signatures (not too great with compound ones but can work them out given enough time)
I know the chords within keys and what scales to use.
Blues scale.
I know the formulas to create modes (Ionian to Locrian, don't know modes of the melodic minor I think it is (Super Locrian and stuff like that) though I don't know exactly how to use them so I don't).
I know plagal and perfect cadence (like why B7 to Em sounds more final than Bm to Em (i know of a couple more but haven't tried to use them yet)).
I know a little about modulation (pivot chords but thats about it)

I can't think of any of stuff right now. I'd like to learn more about borrowed chords, modulation, and stuff like that. What do you think I should focus on?
You know a lot. Can you apply it, in real time to the guitar or whatever instrument that you are playing? Do you know where you'd likey use some of these things, like where to use Melodic Minor, or Locrian?

Modulation and harmonic analysis sort of work together, but one way to do it is use a V - I or even the ii V I of the target key.

Sub chords - study the common ones - Tritone subs, vi I etc. Not too hard. If you have the foundation that you do understanding might be easy, but I think knowing how you might apply these things would be a good idea.