Lumbar pillows help you sit more comfortably by gently enforcing good posture and maintaining healthy spinal alignment.
Good lumbar-support pillows provide consistent back support and comfort even during long sessions in a chair / car seat. They are also easy to set up and adjust
How to know whether your office chair provides good lumbar support: Sit down in the chair with good posture, align your ears and shoulders squarely over your hips. If you have natural contact between your lower back and the back of the chair, such that the normal S-like curvature of your low spine is maintained, it’s a good chair. The chair shouldn't overaccentuate the natural inward curve of your back. Moreover, you shouldn't need to push your lower back into the chair.
Keep in mind that however great a lumbar-support pillow you use, you should never sit for longer periods as it is bad for your health as well as your posture.
The best lumbar-support pillow: LoveHome Memory Foam Lumbar Support Back Cushion (best long term comfort, easy secure, adjust, and wash)
The second best lumbar-support pillow: Everlasting Comfort 100% Pure Memory Foam Back Cushion (more firm than top pick)
The best lumbar-support pillow upgrade: Tempur-Pedic LumbarCushion (comes with great warranty, larger profile and firmer memory foam)