We have an adjustable bed and mattress arriving today for my husband Bruce. He has used an inflatable wedge for the past two years which now leaks. It worked well so we committed to the bed.
The nightly elevation helps to reduce his coughing although he is still pretty tired during the day.
Hope you can get your Dad some relief.
Melissa

I have an adjustable bed. I found my coughing does increase at night if I’ll lie flat on my back. We purchased the bed for the purpose of helping my cough. I start out with the bed flat and sitting erect with two pillows behind my back. When I begin to nod off, I will slide down onto my side and raise the head portion a small amount (two pillows would have the same result). Side position helps. By morning I can most always lie on my back. A problem with the adjustable bed is ours lifts the entire bed so my husband must endure the position as well. I learned too late one is made for each side to have a choice of positions. Also, when the head section is raised there is a dip in the center of the bed. Actually when both head and foot are raised together a larger dip in the center occurs. So folks with any back discomfort might find it a problem. After having the bed for over a year, I find it has Not helped my nighttime coughing. Side sleeping has.

I had sinus surgery also then invested in a adjustable bed. It has helped a lot with being able to sleep. Hope he gets some relief