It's well out of your budget but my Herman Miller Embody is wonderful. You could always ask Tsunami Axis (UK importers) if they have an ex-display model going cheap.
As others in this thread have mentioned get a refurbished Steelcase Leap. They are about £150 off eBay and the one I got looks brand new.
Proper ergonomic chairs and just about everything is adjustable.
Very true,Depends on your back dude, i read that report when it came out, and adjusted my chair to suit, my back started to get a little stiffer then cut to one month later i was stuck in bed unable to move my back had pretty much seized up, took months of not sitting in the PC chair to sort it out. Everyones back is different, but sitting upright is certainly better for mine.
I know what ya mean about having a car seat at your PC, i almost gave in and bought a lazyboy type seat when my back was at its worst.
It sucks. I even moved my sofa up to my desk once because my 9 year old chair was starting to hurt my back so much. I just bought I nice leather one with lots of cushioning with a tilt lock (I think tilt locking is really bad for you but it's so comfy ffs)
It's a lot more comfortable and I can sit for longer but I will still get pain after several hours. However if I go swimming or whatever for an hour or so I can sit on anything for the rest of the day without any pain at all.