“As is the mind so is the body,
As is the body so is the mind.”
We come to our practice of “Yoga Nidra” in the śavāsana posture (lying down) There is no right or wrong way, especially when you are starting out. Make yourself comfortable, use a blanket, cushion, eye pillow, you may wish to pop a bolster under your knees.
Do what feels right for you. “The room should be neither hot nor cold, and there should be no breezes or drafts directed toward the body. Sight stimuli are eliminated by simply closing the eyes.”