What's the most comfortable reading chair?

Stressless are pretty good and any place that sells them should have a decent collection of other high quality chairs. You should try them in-person though, because its not a one-size fits all situation.

https://www.stressless.com/en/services/find-dealer

Probably an overstuffed leather wingback by the fireplace, on a thick pile carpet next to a side table holding a snifter of brandy.