Hellos to those visiting this topic

Posture comes up in a perennial way, and posture will always come up, because the posture prescribed in doing zazen, otherwise translated as 'sitting meditation,' and the posture recommended in shikantaza, otherwise translated as 'just sitting' is dynamic.
it is an active sit, and that is why it is sit ing and not seated zen.

there are small, constant adjustments to the posture. This living body can't be 'still' even when it is being still.
even the inanimate things around the space I find myself sitting in is in constant subtle flux.
the light in the room changes from when I start my sit to when I end my sit, the walls, the carpet, everything is changing temperature, everything is breathing, so to speak.

due to knees which subluxate and dislocate (rather too easily, if you ask me), I have found sitting with a small support pillow under each knee works well. I have my stable 3 point position--knees pressing down, in contact with the floor via the support pillows, allowing the spine and back to maintain full erect posture; without the knees in contact with the floor, I do not have the same ability to maintain an erect spine, not in the same, balanced way.

There is a dynamic, active, 'ing' to the posture. At one time (injury to foot) I had to sit on an exercise ball -- very good substitute, it turned out--very dynamic-- how does one keep a round object still? constant subtle adjustments!

put the 'ing' in sit

I can't recommend it highly enough

'ing' suggestions from others?