This lumbar support cushion (lumbar is the lower back) attaches to the back of your chair. When seated the lower part of the spine should curve inward. But slouching rounds the spine out.
This compresses the lower back nerves and weakens the ­muscles, leading to pain. Support cushions sit in the lower back, where they gently apply pressure, keeping the spine in the correct position.
You can improvise one by rolling up a towel, but the beauty of this product is that the support sits on a pivoting arm, so it moves as you do.