I stopped using Amazon a while back, but it was where I got all my books for a long time. I do thriftbooks mostly now, and try to buy directly from publishers when it’s a newer book, but I’m always interested in finding new spots to cop some sweet books.
The protagonist hops through a multiverse when falling asleep so seems like Doors of Perception might’ve been the inspiration for the idea. It’s a very fun light sci-fi read.