Understanding good computer ergonomics is important. Lots of research points to sustained sitting postures as a source of simple lower back pain. Poor computer posture can also lead to other problems too such as neck and shoulder pain and forearm and hand problems.
One of the easiest things you can do to try and reduce postural stress and strain is to sort out your work station and get your computer posture as well optimised as possible.
I have met so many people who manage with any old thing; the chair should fit the person, so experiment with different types as not all chairs will suit you. A key point though, if you are using a conventional chair, make sure it has a good solid base, is height adjustable and that you can alter the angle of the backrest.
Make sure your lower back is well supported, either with a lumbar roll or by having a decent support already built into the chair. The *Mckenzie Lumbar Roll is the lumbar support of choice for most physiotherapists. I own one and have had the same one for nearly 20 years (its very shabby after all that time but I love it). They come in a variety of degrees of firmness and width. Experiment to try and get the right size. A common mistake is buying one that is too big. More is not always better - it depends on your shape.

To achieve this you must have an adjustable monitor, both for tilt and for height. If you have to twist or turn to see your monitor this is very bad news!
Your upper arms should be relaxed and vertical if possible.In order to achieve this your keyboard needs to be separate.
Unless you have a separate keyboard and mouse and can get the laptop monitor up to a decent height you will never get good computer ergonomics using a portable machine.
I find that often in offices, people share chairs and computer workstations. Whilst this is not always avoidable it is not good practice either. Everyone is different and your workstation should be set up for just you. Failing this, take time to readjust each time you use the computer gain – it will be worth the effort.
Employers have a responsibility to keep you safe, that includes making sure your computer ergonomics are correct for you. Many companies will offer a computer ergonomics assessment and give advice tailored to you.
I can't recommend a specific chair for you but take a look at these *Aeron Chairs by Herman Miller. I have heard a lot of really good reports about these. The general feedback seems to be that they are highly adjustable and comfortable but that it important to get the sizing right for you. There are some good tips for sizing in the readers review section so check there if you are thinking of taking the plunge and getting one of these.
The Importance of Posture
Why posture matters
Correct Sitting Posture
Best Mattress and Sleeping position
Proper Lifting Techniques
From Computer Ergonomics to Lower Back Pain Toolkit Home Page
23-Sep-2011