If you go with your .org you wiil (IMHO) regret it because many visitors who intend to visit your site and type the address in will end up going to the .com neighbour which may end up being a competitor.
Also .org is intended to be a non-profit making organisation.
In the big picture a domain name being specific is not so vital.
Remember the most successful selling site in the world (probably) is amazon.com and Amazon has absolutely nothing to do with Books.