Steelcase Leap V2

The Leap V2 is the chair that ergonomics reviewers most often name as their first suggestion for anyone whose desk job aggravates lower back pain, and it earns the top spot here on the depth of its adjustment rather than looks. Steelcase's LiveBack backrest is designed to change shape and flex with your spine as you shift and recline, with a dial-adjustable lumbar firmness that lets you tune support to your own curve rather than a fixed pad. Crucially for back pain, it pairs that with adjustable seat depth and 4D armrests, so taller and shorter users can both get thighs supported and elbows loaded off the shoulders. It is expensive at an indicative ~£1,000 new (and frequently discounted below that), and it is a conventional upholstered chair rather than a breathable mesh one, which is the main thing you give up versus the Aeron below. But for sheer adjustability-per-back it is hard to beat, and Steelcase's long warranty on the frame and mechanism makes the outlay easier to justify over years of daily use.