I can share my personal experience with you. I'm a 31 year old guy with a sedentary job where I need to spend hours on my computer. I developed lower back pain around 6-7 years ago and more recently upper back and neck pain. I went for Physiotherapy and felt relieved from the pain. So my answer will be based on recommendations of my physiotherapist.
Before telling about the chair I would share about the ideal posture with the help of the following figure
This figure appeared in a google search and is closest to the physiotherapist's recommendation.
Based on this posture the points to note when choosing a chair is:
- Height should be adjustable such that your eye level is as indicated in the figure. In addition your feet must be flat with thighs supported on the chair and parallel to the floor. With a laptop, maintaining eye level can be a problem. IMO, you can use a wireless mouse and keyboard and keep the laptop at a suitable height.
- Arm rest may not always be good. It should not be so high that it blocks you from moving closer to your desk. Ideally you should be close enough to the desk so that your elbows rest on the desk. Height of the desk should be such that shoulders are relaxed and don't feel pushed up by the desk. Sometimes if you rest your arm on the arm rest and use a mouse placed on the desk, the edge of the desk can put unnecessary pressure on the wrists.
- Back rest should be flat with slight curve for supporting lumbar back. If needed you can use a lumbar back support or a cushion for the purpose. The ideal angle for the backrest (from horizontal) should be around 100 degrees so that you are almost upright.
- In addition the seat should not be too hard as it can put unnecessary pressure on the hips.
In addition, I was recommended not to slouch or lean forward. For this the screen should be at a right distance and font size should be large enough for you to read while sitting straight (leaning back on the chair). Moreover take regular breaks from work and walk around a bit.
Note that this is what my physiotherapist told and I felt benefited. I haven't read any studies on this, so scientific references are welcome.