I'm not exactly up to date on the current market but I can offer this:

Most eReaders have .epub capability, with the notable exception of the ones made by Amazon so you have a pretty wide selection to choose from. I have a Nook Glowlight 4e which serves me well. It's very barebones and has downright abysmal notetaking features but it has a backlight, physical buttons (super underrated), a long battery life, and font options so it's fine for lesiure reading. More modern devices have things like higher screen refresh rates, higher resolution, and more app connectivity. Note that some devices are compatible with ebook lending systems run through public libraries, if that interests you then by all means look into it, one of the best ways to support your local library is to use their services.

All that being said, if you're anticipating only loading books on manually then you would be fine with getting an older secondhand device on the cheap. IMO the most meaningful difference between "obsolete" and modern devices is access to online bookstores.