There's a really good book, "Saucerful of Secrets: The Pink Floyd Odyssey", published in 1992. A friend loaned it to me in 1994 and I read it cover-to-cover in about 2 days. There was background that I never would have known, not having been there at the beginning. According to the book, Floyd and Soft Machine were two major hot acts when they appeared, and routinely lured each others crowds away. Hard to imagine now.
Thanks for the recommendation, I just ordered a used copy from amazon for around $10. It will be added to my stack of books to read.