https://therapia.cz/

Not sure if you are gonna be able to get it outside the Czechia, but this is really the only chair that ever helped me.

Herman Miller is a good chair, but it just allows you to sit right, Therapia chairs are made to force you to sit right (making any other way of sitting highly uncomfortable).

At first, I was not able to sit in Therapia chair for longer than 1 hour as it was literally stretching all my shortened muscles.