If you have not checked out the series "For Beginners" a nonfiction, graphic, book series, it is worth a shot. They cover everything from philosophy to linguistics. They are open to submissions and you can submit text without illustrations if you are a writer. Really study their book line: I did so carefully and still missed the mark.
I sent them a proposal, which to my great disappointment was rejected (because I spent many hours preparing it for one thing and I was really excited about it for another) but the good news is they replied the same day they received my proposal. That is the best turn around I have ever had and I would submit to them again.
Hope this helps someone.