I have to agree that the Paperwhites have gotten about as good as they're likely to get in the near future. Still, I've also been wanting something smaller. I've been reading more and more on my phone and finally I've read my last 6 books exclusively on my phone. It was pulling the battery down so I got one of these:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
It's a $50 phone. It works with my service provider although I don't have service on it. If my regular phone fails I can fall back on this. In the meantime I'm using it as my ereader and it's excellent for that.
It also has a user replaceable battery so with any luck I should have it for a long time.
Barry