As others have said, Kobo is the goat.

I have a ClaraHD. It's not huge, but is about the size of a paperback, and you can probably pick one up pretty cheap these days. I've had mine since 2020 and it's still going strong.

As an added bonus; while it's a bit of fiddle to set up, if you already have a server at home, you can run something like Grimmory, which will enable you add books to it and sync them wirelessly with a Kobo. These days I literally only ever plug mine in to charge it once every few weeks.