Kobo Libra 2 the right choice
Up until then I'd been reading on my tablet, but a e-reader is much more practical and comfortable for the eyes, and lighter too. I chose the Kobo Libra 2 because it's so easy to hold, with the screen shifted to the left (or the right if you're left-handed, as you can tilt it either way). This means you can hold the tablet with one hand and your thumb intuitively falls on the button to turn the page. The slight edge around the perimeter makes it easier to hold. Good ergonomics, then, and very satisfactory screen quality (I have no comparison...).
I'd recommend this e-reader, which fits in an inside pocket and has a very comfortable screen size.