Sitting is a position, not a personality
Alternate. A sit-stand desk is nice. A counter and a chair is enough. The win is changing shape more than once per release cycle.
If you stand, do not freeze. Shift feet, calf raise, unweight a hip. Standing still for three hours is just a vertical chair.
If you sit, keep the pelvis from rolling into a full slouch for the whole movie. You will slouch. That is human. Reset when you notice, like you would restart a stuck client.