First thing, check with your local public library.
They are most likely going to already have a free app to use with your library card. (If you don’t have a library card, get one. They are free and it is very illegal for libraries to give your data to anyone without a court ordered warrant).
My library uses Libby, and it’s great for the most part on any smart device.
If you do end up licensing (and it’s a license, not a purchase). Amazon’s Kindle store is good and has some exclusives.
I’m a librarian who orders books for this section. It is really weird to go from UFOs and Bigfoot to programming with php and Linux books.
A “perk” of Dewey decimal system