Exon's suggestions are good. Some other ideas: If the books are fiction, you could use, "novels". Literature could be used. i.e., "In scientific literature...". "Paperbacks" by itself refers to paperback books. "Print edition" refers to a regular paper book. Books can be called texts. I'd stay away from "tome" unless it's a large dusty old book you are referring to. Ebooks are more difficult, sometimes they are referred to as a electronic reader or e-reader, sometimes by their brand name - I'm always talking about my Kindle. I'm out of synonyms, I hope this helps.

Hey Man, how about "reading materials " "reading matter".I've seen them both. But I need a favour too.