The best chair for low back support is one that fits you well. I recommend buying a chair that has the most adjustment spots possible so you can adapt it to your body.
The ideal position for your spine is:
1. The seat is low enough so your feet are flat on the ground
2. Knees should be at 90deg
3. Hips should be at 90deg
4. Your back should be flat against the back of the chair
5. If you want a mild back support, use a cushion like the one described below, or a small towel roll
6. Your elbows should be able to rest on the arms without leaning forward or shrugging your shoulders up. The keyboard should be positioned so you can easily type.
7. Your computer screen should be 1-2 inches below eye level. Avoid jutting your chin out or squinting at the screen.
These are starting recommendations, adjust as needed to help you find the most comfortable, sustainable position. Even when you find this ideal position, I generally recommend people standing/walking around every hour for at least a couple of minutes. Even with the best sitting posture, sitting causes compression through the spine.