I have a book called Hellbirds: The Story of the B-29's in Combat, by Wilbur H. Morrison. He was a bombardier with the 20th Air Force, from its time in India, China and eventually Tinian Island. I really enjoyed the book.
I bought my copy in 1979. Not sure about its availability now.
He's written other books about different units, and different wars, but Hellbirds is the only one I've read.
Cheers,
Mark