Hi-- I own 2 of the "standards" on the WF's:
"The Expert's Book" by Paul W. Schmid and
"Washington Franklin 1908-1921" by Martin A. Armstrong
You can find both on
ebay, I think that the soft cover Armstrong book would cost you less, and in my opinion is the best.
I've read the Armstrong book from cover to cover, and instead of being a technically-written reference, it reads like a story, and makes it easier to understand how all of the varieties came about and why, and I think anyone could read and understand it.
The Schmid book, I have in hard cover, and it's tall, hard to fit on a shelf, but the pictures are much larger also.
Hope this is helpful-- Good luck, Ray