When I was taught to meditate forty-four years ago the usual position of sitting cross legged on the floor was extremely uncomfortable so I tried it lying down. Much better. Since the intent was to connect with the Stillness within it made more sense to focus on this and not spend time and energy battling remediable discomfort.
This made increasing sense with the further realization that the spine is best kept straight and the body relaxed. In a supine posture with a support under the head the backbone was aligned and contact with that nourishing, supportive earth maximized.
A major epiphany later occurred with the realization that if the spine is indeed straight and the body relaxed and then one inhabits the body – the meditative state is immediately experienced. I had spent many years attempting to control the mind with the mind with enough success to keep me chugging along (that natural state of Stillness is bliss) but inhabiting the body was an expansive leap in the journey and allowed meditation to occur anywhere, anytime.
Meditation is a tool and finding the 'one' that best suits makes the 'job' easier.