I only read DRM-free books, and I just use a 5-year-old Kindle Paperwhite. You can use Calibre to convert ePub to mobi, and then view it just fine on Kindles.

You can also get a used Kindle Paperwhite for pretty darn cheap. I wouldn't recommend going to earlier Kindle generations prior to the Paperwhite, because they didn't have backlights which makes reading in low light conditions (like bed) a lot less pleasurable.

I already have a Paperwhite and it's quite good, but the plastic degraded and is now sticky, the CPU is slow and doing anything takes a while, and it doesn't have the very handy buttons earlier versions used to have. I was wondering if there was anything available nowadays that was much better, basically...

Oh, hrm, I have no idea. My Paperwhite is in a better condition than yours and it's good enough for me.

I really wouldn't mind having physical next/prev page buttons, though. Having to touch or swipe the screen is kind of annoying. I feel like that's a step back in UI from previous gen devices.

Yeah, I have no idea why they removed them. The swipe combined with the high response time means I never know if it registered the swipe and always go back and forth in an effort to change pages.

They probably saved some trivial amount of money on manufacturing costs by removing physical switches, seeing as how they were implementing touchscreens anyway for the rest of their interface.

Smartphones initially had physical buttons that have gone by the wayside now, but at least their screens are much more responsive!

For good ereaders there's Kindle and Kobo. Kobo supports DRM-free epub, but in practical terms, it doesn't matter a whole lot with Calibre to organize your library and convert to your format of choice.