The Kobo Aura H2O seems to suffer from the same "sudden death" issue I had with the Kobo Aura HD. And it is an older model. Although you've a good point for the bigger screen: 6.8" versus 6".
IMHO 7" is ideal for reading, but 6" will also do nicely (I also still using my trusty PRS-T1). But then, you cannot have it all, can you?