I don't want to contradict Harry, but just mention, as this is very important for you, that eink readers are fine to the eyes.
Realistically, you can only use a 10" device. All the other readers are too small as most pdf files are prepared for A4 or letter size. The best and almost only choice is the Onyx Boox M92. You can find a lot of information about it in our Onyx subforum (
https://www.mobileread.com/forums/forumdisplay.php?f=220).
The other great advantage is the much better battery time.