I have a kindle from like a decade ago. It works fine. I just today had the thought as I was carrying it from the beach “why would anyone replace an old kindle?” So my suggestion is get the cheapest oldest model you can. Last week I updated my self hosted ebook library so I have calibre, calibre-web for a nicer front end, and readarr all working in tandem; it’s just about perfect. Books arrive magically on the device once they finish downloading and they download the instant they become available. I don’t know what else I’d want except for maybe a back light. But reading with actual natural light is a pleasure too.