Probably not what you're looking for but I've been using a yoga ball for the past several months.
Main reason being that I didn't want to spend thousands on a proper chair AND a standing desk and I had started to develop sciatica from my previous chair + desk combo.
For what it's worth, it's definitely helped my sciatica issues, but I am still struggling to maintain a correct posture for my back and I have to take breaks from it.