I've been using the Swopper (https://www.aeris.de/en/swopper/ https://www.aeris.de/en/swopper/), a swivel stool which is similar to sitting on an exercise ball.

I've been using the Swopper (https://www.aeris.de/en/swopper/ https://www.aeris.de/en/swopper/), a swivel stool which is similar to sitting on an exercise ball. The stool is built on top of a spring fitted shaft, which means you can _bounce_ up and down while sitting. Additionally the shaft is attached to the base with a free swinging joint, meaning that you can rock around 360 degrees. The whole design rational is about keeping your legs active while you are sitting. In order to sit on the stool, you need to continually balance yourself using your legs and back. I've had a few friend sit down on it, completely unaware of this, and fall off immediately. It can be tiring but really I've gotten use to it and can sit for hours without problems. The stool has helped a lot with my back pain and improving my posture. I have two versions, one with and without rollers. The one without rollers is nicer to use, as the rollers don't always _lock_ meaning as one is bouncing around the stool base might shift. Aeris also make a more traditional desk chair based on the same principle, see https://www.aeris.de/en/3dee/ https://www.aeris.de/en/3dee/. The price is about $1K for the Swopper, and for me was totally worth it! Also it's built like a tank and weighs 10kg.