I've tried half a dozen chairs ranging in price from £30 up to £150, they were all terrible and all broke inside of 12 months.
So my advice right now is either go really cheap (£30) or go really expensive (£500+). Nothing between the two is worth it. It is a waste of time and a waste of money.
Also seriously think about your desk. My desk was too high and as a direct result I had to depend on the gas-compressor (gas-lift) working fully (to its highest point) or I would get shoulder/wrist strain.
I wound up getting an Ikea adjustable desk. They're less stable than regular desks (I have mine against a wall to stabilise it) but they resolve the height issue.
PS - Don't assume that just because a gas-lift has a maximum weight well above your weight that it will be any more reliable. I got one with a 350 pound claimed-maximum load, and the damn thing still only functioned correctly for six months before it started slowly leaking air.