Avoiding Amazon and books

Unfortunately I do confess I have a kindle, it's about 10 years old, it's clinging on, but it still works and it's not dead- I do struggle to read on it though because my eyes are fucked.

I have to get a lot of the physical copies of books, which is oc expensive, and I need recommendations of here I can get second hand books without using amazon! I don't want to use Amazon for numerous reasons, reasons which I'm sure many of you are aware of, but I'm just unfortunate that I don't have local book shops- how do I get around this whilst maintaining some level of sustainability?

Thank you for any help!!!