Well hello again!
In the hunt for a good chair for you, one thing most people don't consider is that how they work at the desk means they could be sitting on a rock, for all the good the chair is going to do you.
I've seen some rather.... interesting search terms on google- chairs for short, petite chairs, chairs for petite people, chairs for small, chairs for tiny people- you get the point?
If you're not that tall, try using a foot rest. The type that move are great, allowing you actually move your legs while seated increase blood flow and reduce pressure points. In fact, had a 5'2" customer in this morning, the second thing I showed her was a foot rest and she was amazed at the difference in how she sat.
Think about it, when you're shorter, the weight of your legs is not supported, so they are actually pulling your body out from the back of the chair. When your legs are supported, you end up sitting back into the chair as you're supposed to do. It really does feel good, try it!
Here's a picture of the Humanscale foot rest (commercial plug- :-P) available at SitBetter.com
Some like how this rolls easily, but I've found that is not a universal preference. Sitting in a chair with wheels on very thin carpet, floor mat or hardwood floor, some people find themselves actually moving about a bit much.
This is not a problem in areas with thicker carpet, since the chair does not tend to move easily.
If you feel that may be an issue for you, try this sort. It does not move as easily, and there are little rubber stoppers on the legs to keep it stable, in fact.
Again, the main purpose of these is to give the feet a platform on which to support. There are many out there from which to choose, just consider that it's going to help adapt your environment to your body type, which is a far better thing than trying to force your body to adapt to your environment!
For more information (of course, another crass commercial plug!), contact me here or at Sitbetter.com!