(right-handed) I put the bottom right corner against my palm I then put my thumb along the right bezel and the fingers on the back.
(left-handed) I sometimes put the bottom left corner against my palm then I put my thumb along the bottom bezel and the fingers on the back.
If you look at the picture on the basic Kindle
https://www.amazon.com/Kindle-Now-wi.../dp/B07DPMXZZ7 that is how I hold my Kindle, Kobo etc.
One final way, I don't like living fingerprints on the bezel of my PW4, and so I hold it with my fingers on the left edge and my thumb on the right edge like so:
https://cnet2.cbsistatic.com/img/jce...indle-2019.jpg
It is not a stupid question imo, we all go through this problem because the devices are not ergonomically designed (excepting the premium Kindles and Kobos). I had no problem holding my Kindle 3 nor my Nook STR for extended periods of time and comfortable ways to hold them were intuitive. Kindle 4 on they became much harder to hold.
Finally if none of that works for you, try using a popsocket.