For myself, I use the iBooks reader on my iPad. But I should say, I don't buy a lot of ebooks myself. I oversee the ebook production where I work. And iBooks is still one of the best as far as supporting the full epub standard. Kindle has gotten better at that lately, though, I have to admit, with better support for MathML and SVG and better table handling. It used to be trying to view tables on the Kindle sucked ass, but it's not so bad now. I have limited experience with Kobo devices.

I think its weird people read on tablets; seems like it either encourages bad neck posture or your arms will get tired. I read on a windows laptop with "android subsystem for windows" with the kindle app installed. Then I turn the window into the approx. size of a paperback and I can scroll with my mouse scrollbar. So I minimize eye movement and hand/arm movement. https://ibb.co/5xxFSGd

Do you have such difficulties holding actual books?

I just use a Kindle. Good size, decent screen. It works.

I had a fire 8 that I tried for a while. But found the low-res to make it uncomfortable. Is yours a paperwhite?

Yes an older one, but honestly it’s fine. You could maybe get the slightly fancier oasis but it works.

Kindle paper white, a few years old. Almost as good as a book.