Since a car accident is involved and loss of consciousness at the time, have you considered osteopathic care, or possibly upper cervical chiropractic (aka atlas/axis, c1 c2 etc )?
If something was knocked out of alignment , then the best place to start is getting back into alignment. My chiro also did some adjusting to my hips, elbows, shoulder, wrist...he is a long time DC and taken added studies.
There are spinal specialist PTs also.
Have you had any luck with PT at all?
I wonder if a yoga mat would give enough padding for the floor pose?
Odd that the pose doesn't work the same in the bed for you
I know many in the past used to sleep in their recliner quite often as laying flat just did not work for them...
They also had many kinds of pillows to prop arms/shoulder for sleeping , whatever helped.