I have chronic back problems (lumbar) and I've tried dozens of chairs over the past few years from periods between a few hours and a few weeks and I've only found 2 which haven't caused me problems:

Herman Miller Aeron (which I currently use) Steelcase Leap Char (which I used at my previous 2 jobs)

The price for these chairs are high. But given I'm relatively healthy and productive with them, its well worth it.