Don't assume that buying a cheap book on Amazon means that the author is getting less than they would if you bought them in a bookshop. I was told by an author that they get more that way. By the time the publisher, the wholesaler, the bookseller and all the rest have added their profit, each copy of a "real" book sells for several times what the writer receives for it.
I used to feel guilty about buying ebooks, but now my conscience is clear.
It depends on what you are buying. If you want the concept, the plot, the characterisation,the descriptions, the carefully chosen words, the time that has been spent putting it all together and editing, then that is all there in the ebook, just as much as in a paper edition.
If you want the weight of a physical book, the sensation of turning pages and the ability to put a pretty bookmark into the place you have reached, you might just as well as buy one blank book to handle, and turn its white pages as you listen to each story on Audible.