My gf and I had the exact same use case, and decided on Galaxy A7 Lite tablets. They’re perfect for exactly what we want to use them for, which is reading ebooks through ReadEra and reading manga/comics through Tachiyomi. $120 at Amazon.
You get what you pay for - the browser and even some of the UI is a little crunchy, but watching YouTube Revanced or streaming from our Jellyfin server work just fine, and for reading it’s perfect.