The Grandmaster Repertoire series book on the Sicilian by Lubomir Ftacnik was very helpful and I found easy to read. Just Google it.
You should find books on the London as well. IMHO, a book on the opening isn't really necessary. The moves for white generally stay the same for white. That's the appeal of a "system " opening.
What changes in the London is all the defense that black can employ against it. Most "thought " for the white side London player actually emerges in the early middle game. A game collection book of London games might teach you more.
I’ve been looking for a good book on the Sicilian Defense: Accelerated Dragon and other Sicilian books like the Closed Sicilian but haven’t been able to find any that look good. Any suggestions are good suggestions! Also, if there are any books on the London System that you also know of, I’d like those too!