IMO, all bedrooms should have what you call, return vents to give the best effect. Otherwise when you go to open the door, you find a very strong resistance. That tells you, your not getting max flow through. Our M/Bed has a return vent in the walk in robe but the three bedrooms down stairs don't.
The other option is, you have to leave the doors open or partially = not a smart idea.
That's something I may address down the track. Vents in the ceilings, to duct, to the passage or place vents in the top of the doors.
