The two books I selected from the Radcliffe Library are:
(1) "Out-of-the-body experiences" by Celia Green, published in 1968 in the U.K. Celia was the Director, Institute of Psychophysical Research, at Oxford in England.
(2) Astral projections: a record of out-of-the body expereinces" by Oliver Fox, published in 1962, in New York.
Celia's book is a study of a large number of OBEs, while Oliver's concerns his own, personal OBEs.
I am in the process of reading and making notes on both books.