Good to hear you are seeing improvements.
Yes, breaking established habits can be tough and take some time because they are so engrained.
Being consistent is key and it sounds like you are doing that.
Episodes that address sitting position. Improving your sitting position is beneficial.
Improved sitting positioning at the hip and leg will help things up stream (back/shoulders) be in an improved position. You want the whole system to have proper positioning.
Why Sitting Wrecks Your Mad Hip Action
Episode 251: High Skilled Sitting/Abdominal Bracing

Episode 187: Death by Chair. How Much Do Actually Sit?
Episode 91: Mobilize In the Position of Death by Chair
Episode 88: Desk Athlete Hip Rescue
Having a standing position may or may not be an option.
Episode 274: The Standing Athlete