I don't read nearly as much as you, but something like 60 or 70 books a year. I found the opposite to be true: I could find way more that I wanted to read on the Libby library app than on Kindle unlimited. I mostly read SF and fantasy, so I go though all the Hugo and Nebula nominees and read recommendations from places like Locus Magazine. Then I tag those books that interest me in the library app, and place holds (reservations) on a handful of the ones not currently available and start reading ones that are. It seems to work pretty well with zero dollars.