I think the Ergon and similar chairs were and are successful because they are clean designs with good ergonomic foundations….a hard combo to beat.

@Daisy, I believe that if a person using a chair actually has to tilt to the left or right while properly seated in a chair, then there is something wrong with their workstation set up.

Commonly used items should be placed within the primary reach envelope, an arc 45 degrees either side of the midline to a distance of approx. 30cm in front of the body (depending on stature).

Likewise, less commonly used items should be placed within the secondary reach envelope, up to approx. 50cm (depending on stature).

If the workstation is set up correctly like this, with the central axis of screen, keyboard & chair all aligned, then there should be no need to lean forward or tom either side, supported or not.

The force applied to the spinal column when one deviates from the natural curve and upright position increases drastically the more you lean forward or backward, left or right.

In any case, when leaning sideways, the additional forse is not to the rear of your body, but to the opposite side of the motion. A back support won’t help this.

I would stick with the good old standard back support, dare I say it, like a Herman Miller chair. (Note: I don’t work for HM)