Lynn
sleep positioner is good if u want to counter problem of baby turning onto his back. so far i've only seen the babysafe one on the market. the positioner basically wedges your baby tightly between 2 cushions so he does not move about or turn away. for sleeping on side with bolster, u place the bigger positioner cushion against baby's back, let him sleep normally hugging his bolster, then place the smaller positioner cushion in front of him.
to counter flat head, i reposition him by turning his head to the rounded side using sleep positioner. i place his shoulder/upper body -the flat side - on the big positioner cushion, then wedge the small positioner cushion on the other side of his body. so one side of his body - the flat side - will be raised and resting on the big cushion, and his head will fall to the other rounded side.