Consider that, when sitting, support is not a matter of what comes behind the back, but of what comes under the hips, to help prop the hips to roll forward onto the “sitting bones”  This is to prevent the lower back from rounding, which forces those muscles to hold the body up, which is not their job, creating muscle strain immediately, sapped energy and dullness and stupidity immediately, and, with consistent practice, herniated discs over time! A blanket or Yoga block, or any improvised prop is useful to allow the hips to be even with, or higher than the knees, so that there is no strain on the abdominals and thighs as they establish their role in holding the body without strain. The lower back is in it’s natural curve, indicating a lack of tension and a pure flow of energy through the spinal column. The hands, palms down on the thighs, establish support with ease for the side waist and ribs, from the sitting bones to the collar bones.  At this point the breath is free to move the body into position.  Go on to  the “Breathing” page...