https://www.amazon.com/Milliard-Supp.../dp/B00U9T3HWU
A lumbar support cushion at $20 bucks, will be better for your back than ANY chair you can buy. The cheap chairs people are shown in pictures are fine! but they need to be replaced regularly, say every 2 years, and they certainly need the cushion.
memory foam is memory foam and having an 100kg plus ass sitting in it all day will fuck it out in a couple of years 200 buck chair or a $3000 one, don't get caught in the sales hype.
btw I've had multiple previous back surgery's, been pain and back issue free for 10 years... I know my chairs, tried many over the years in all price ranges... get a cushion.