ONYX BOOX makes several different models, including some with color screens and most with reading light built in. They also have fantastic battery life. I have a Poke 2 which has lasted a month of active reading before needing to be charged.

These are basically Android tablets, so data transfer is not locked down. You can put whatever you want on it.

I know you said you don't care about apps, but on these you can run basically any Android app (within limits of e-ink screen functionality), including useful stuff like Obsidian for notes and Syncthing for syncing files across devices.