E-readers — What size is the best for PDFs?

I am a researcher. That means I have to read academic papers and books. Unfortunately, I don’t really have room for them, and even when I print out academic articles, I tend to lose them along with my notes. To be honest, I am not the best at self-organization. So it has long made sense for me to read as much as possible digitally. But that has its own problems.

Perhaps the biggest problem with regular computer or tablet screens is that they cause eye strain and eye fatigue. My very lay understanding is that there is more than one cause for this…