I sometimes can’t sleep due to stress or sickness. So I have a book on my nightstand for this situation.
It is a field guide to trees in my area. It is very boring and I’m not retaining much of what I read at 3:30 a.m. The point is to sit in a chair and look at trees until I feel I can fall asleep again.
I usually just read whatever (fiction) book I’m reading. I don’t need it to be a particularly boring one. It varies a bit how far I get but usually not that many pages before I know it’s time.