Spent all kinds of money on chairs over the years. I do have my share of back problems having screwed it up pretty-bad when I was a kid, but it seems that each person's back issues present a unique set of issues for an individual, so what works for me might not work for you.
Ironically, The chair I can sit in for hours at a time and am most comfortable in - the chair I swiped to stick in my music room because it is my favorite chair - is a $50.00 cheapo mid-back Amazon-type office chair which I never attached the arms to. I like it because I can actually move around and flex my back while sitting in it, whereas some of the bigger, fancier chairs - like the ones I have at work, hold me to a position and don't allow me to arch and flex my back to different degrees.
The big thing for me is my ass.. Okay, that might have been mis-put. But, many of these chairs, after a while, the memory foam will compress and you are sitting on the equivalent of a board. But this little cheapo chair doesn't bother me like that either. Could also be that I can move around on it and not be fixed to a position where """"flat ass"""" becomes a very-real and uncomfortable thing. :0)
..One you can kinda check for. If you like to move around a-lot, and this solves some back issues for you, then a chair with backrest that doesn't reach your ears might be for you. Whether or not flat ass is gonna be an issue though, only time will tell :0)
either way.. removable arms.. removable chair arms that is. :0)
Best of luck finding what you need
here.
edit: ..might go without saying, but I also use an adjustable foot-rest. That might be helping, as well.