How to select the sitting chair to help you get positive posture?

I use desktop usually at home or at school and due to negative sitting posture I was suffering from shoulder and back pain for long, until I realized that something was wrong with my chair and sitting position. I searched the net to look for information and suggestions for this purpose and I was happy to find the stuff.
Right now I am using an ergonomic chair while I am following the positive posture techniques to get relief from back pain. I have collected the relevant information at this post for my blog readers. Now in this post I want you to suggest and offer tips to select the sitting chair which can help you get the most suitable position to reduce shoulder/back pain.

Positive sitting posture means the proper way to sit at a chair while working beside the table. In my previous post I have mentioned some causes for should and back pain associated with negative sitting posture:
Link How bad sitting posture causes shoulder and back pain?

Sitting posture is an important factor in both your health and performance in the workplace. One of the main factors identified as causing an increase in back problems is computer and gaming use. A New Zealand study found that workers who spent an inordinate amount of time sitting at their desks were at a higher risk of developing deep vein thombrosis (DVT). Workers who used computers while sitting were at an even high risk.

The best way to reduce pressure in the back is to be in a standing position. However, there are times when you need to sit. When sitting, the main part of the body weight is transferred to the seat. Some weight is also transferred to the floor, back rest, and armrests. Where the weight is transferred is the key to a good seat design. When the proper areas are not supported, sitting in a seat all day can put unwanted pressure on the back causing pain. By selecting a sitting chair which is designed on the basis of ergonomics can help you get the positive posture and reduce the risk of shoulder and back pain.

The qualities you need to look for a sitting chair 

• A chair that allows you to take an upright seating posture. The angle between your upper and lower legs should be about 90 degrees and your feet should be resting (flat) on the floor.
• It should also have a sturdy frame , a great deal of support, especially in the lumbar region, and padding that has some give and supports your body without losing shape.
• It help increase back and neck support to help improve posture and prevent slouching.
• The seat should have enough width and depth to support user comfortably. The depth (from front to back of the seat) needs to be enough so that the user can sit with his or her back against the backrest of the chair while leaving approximately 2 to 4 inches between the back of the knees and the seat of the chair. The forward or backward tilt of the seat should be adjustable.

The material on the seat and back of the chair should have enough padding to be comfortable to sit on for extended periods of time.
• Lower back support in a chair is very important. The lumbar spine has an inward curve, and sitting for long periods without support for this curve tends to lead to slouching (which flattens the natural curve) and strains the structures in the lower spine.
• The backrest of an ergonomic office chair should be 12 to 19 inches wide. It should be able to support the natural curve of the spine, again with special attention paid to proper support of the lumbar region.
• The height of the backrest should be adjustable.
• The backrest should be adjustable for movement backwards or forwards.
• The chair should have capacity for 360 degree swivel.
• The height of the seat should be adjustable.
• The seat should have a non-slip surface. 
• Make sure the adjustable levers are not in a position where they might interfere with daily work.   

Useful links:

* Computer Chair Buying Guide A Step-By-Step Guide
* Free Stretching Exercise Reminder for Computer Users
* You Might Want to Sit Down for This