Plastic (although not ambient friendly) is more peaceful, as you can bend it. A wooden chair has the benefit that you can sit more on the edge without falling back, cause I’m basically talking meditation sitting position 101, here, your spine should rest like “a stack of gold coins”, and tilting the hips back like on the edge of the sit helps put the spine straight, so there’s no stress and you can just rest in the position for long periods of time

Really peaceful for me would be like a stiff zafu and sitting cross legged (with butt near the edge of the seat)