If you spend lots of time in front of a computer, it's important to have a decent chair with proper lower back support if you want to preserve your back. You may not notice or care now, but you'll notice it in a few years! Prevention is better than cure & all that.
In many offices in the City of London, it's quite common to see Aeron chairs (with mesh seat and back - public domain photo shown above), which are supposed to be ergonomic and have won design awards.
But, a physiotherapist who treated me for my back recommended that I stop using an Aeron chair. The issue with those chairs, he said, is that you can't adjust the angle between the seat and the back - it's fixed, so if you tilt the seat forward or backward the back tilts by exactly the same amount too, and vice versa.
I was using an Aeron chair in my office up to that point. I don't know if that chair caused my problem; I suspect there were other contributing factors like general bad posture, but I took his advice to change my chair, given how many hours a day I spent at my desk.
The chairs he recommended instead were RH Chairs, which seem to be available only in Europe including the UK (there's an importing business opportunity for an American!).
So I got an RH office chair, the RH Logic 400, pictured below. Almost everything is independently adjustable - there's even something at the back that you can squeeze to pump up or decrease the lumbar support! I'm very happy with it.
I also heard a different physiotherapist (at a talk on practical office ergonomics) recommend RH chairs too, which is a comforting extra independent endorsement for RH.
(I can't however recommend RH's UK or head office PR departments, or perhaps it's whoever monitors emails to their email@example.com and head office email addresses, as both offices failed to respond to my email requests for permission to reproduce a photo or diagram of their chair from their website for this review - PRfail definitely!! A photo of my own chair still wouldn't be detailed enough to show how flexible the RH is. So I'm just showing the little Amazon preview.
Their website at least is decent, so go there if you want to see pictures of the chair and the kinds of adjustments you can make to it (here's a Flash example) - they have a good wizard which walks through what model of chair would suit you depending on the environment it's to be used in e.g. Office/administration, Industry, School, Counter/reception, Control room/24 hr use, Laboratory work/medical, Dental, even Hairdresser.)
RH chairs aren't cheap (a couple of hundred quid or more), but neither is the Aeron. Think of an ergonomic / posture chair as a long-term investment for your health. It's possible that some employers, if they're made aware that you have a back problem, may be willing to pay for a decent chair in order to avoid the risk of being held responsible for health & safety issues. Unfortunately, I don't know if they'd be willing to buy you a decent chair if you don't already have a back problem, even though prevention is better than cure.
Also, at least whoever you buy an ergonomic chair from should be able to help set it up for you for free - which is very, very important. It's no good getting an adjustable chair if it hasn't been adjusted (by someone who knows what they're doing) to fit you properly, as everyone's body is different; a poorly adjusted chair can be as bad as a bad chair. So do make sure you take advantage of that service.
My point is, once your back goes, it'll never, ever be the same again - back pain will always be a looming threat. A "slipped" disc isn't in fact a slippage, something slipping or moving out of place (like a dislocated shoulder); "slip" is a misnomer - it actually involves a physical tearing of the membrane. While the rupture will hopefully heal, it'll never be as good as having a totally undamaged disc.
So if you use your computer a lot, or just spend a lot of time sitting still at a desk, you owe it to yourself and your back to sort out a decent chair for yourself, R H or otherwise (there are other options) - sooner rather than later. Or you may regret it.
Note: I am not a physiotherapy or medical expert, this post just reports on my personal experiences. Different chairs may suit different people. You should seek advice from a suitably qualified health or medical professional if you have back pain issues (and take with a pinch of salt the sales pitches from shops that supposedly sell ergonomic products, obviously many of them mainly want your money!).