OT GFP, I was just recommending a variation of the decade(s) ago Ann Landers advice to the sleep deprived spouse (sleep deprived because of the snoring partner). Before resorting to separate bedrooms, she recommended sewing a tennis ball into the back of a pajama top, in order to make it uncomfortable to sleep on the back. The 2 tennis ball variation in a sock, safety pinned to back of a preferred sleeping garment could be adjusted to maximize the incentive not to sleep on your back. Cervical spine support does not come into play.
I wish you well. This is not a trivial issue, but it is difficult to isolate OSA from the associated causative risk factors for cardiovascular disease. Increased neck and abdominal circumference often live with OSA as well as diabetes/high blood pressure/metabolic syndrome etc.
Sorry, GFP, I did appropriate your SA projections, in response to a rare reasonable post at YMB.