@Andrew Baker:
I have a long standing back problem, like a lot of people I think. The trouble is that talking in-depth to various medical professionals over quite a few years now, as I understand it, in a nutshell, all back problems are the same and all back problems are different (if that paraphrasing makes any sense at all)!
Here's what helps for me:
1. Make sure you haven't got anything like a wallet, mobile phone, etc, etc, in your back pocket when sitting down. This applies very much when driving too;
2. Get a wedge of HIGH DENSITY foam rubber made up (orthapedic foam is expensive, I've found that the old-fashioned hard rubber/horsehair packing material works fine, IF you can find it). It needs to be cut to fit the seat of the stool or chair, and needs to be (in my case) about half an inch thick at the front (where your legs are) and about three inches at the back (where your backside goes). When sitting down make a conscious effort to centre your body weight on the cushion and make sure that you are NOT leaning on the chair back rest, nor too far forward;
3. There's an inflatable physiotherapy rubber "pancake cushion", completely round, about ten inches diameter but only about one inch when partially inflated (which is all that is needed - hard inflation is a no no). Again when first sitting make an effort to sit centrally and make sure your back is NOT resting against the chair's back rest;
In any case, make a conscious effort to stop what you're doing about every hour or so and just get up and walk around for 5 mins or so before starting work again. I was a devil for this and after my op and the physio first told me about this, in the end I had to resort to setting an alarm clock for once an hour to make sure that I did get up (I tend to get "lost" in what I'm doing and otherwide find that 3 - or more - hours later, when whatever it is is done I stand up and then find out that I now have a helluva back ache - don't notice it all that much when concentrating on something else)!
In any case, if yoiu're like me none of the above will remove your back ache, only reduce it to an extent.
As above, "your mileage may vary" with any/all of the above - all backs and their problems are different.
Best of luck mate, back ache's "a bloody awful PITA" isn't it?!
AES