I have to say meditating sitting upright is quite different from laying down. Body scan feels great in savasana (laying on your back) and it will definitely relax and nourish the body. But when we lay down, purely from the perspective of the body physiology, mind tends to be not as sharp and awake. For transformative practices I prefer sitting upright. If you can sit upright fairly comfortably, erect spine really makes a big difference in your level of "wakefulness". I'd say try it both ways a few times and see if you notice any difference :) As Buddha said "don't believe. experience for yourself". As crypto traders say "don't trust. verify"