Seat back all have provision for a rear head rests. Grab some black tubes from a junk yard yard seat. If they are trashed, pull up the covering. Push the tab and tap them up from the bottom. Seeing this on other seats will help understand how this works. (I got my tubes from a back seat, so some speculation on compatibility front to rear).
The rear seats have holes for three head rests. Pull the seat out with a torx driver. Unfasten the covering connector on the bottom edge, and loosen the side velcro. Put a thin screw driver up the front of the metal between the pad and metal. The first hole on the metal cross brace is 20 inches in, so the forearm will go in as well. The head rest post angle forward, so tilt the driver to find the upper hole. Push through cloth, cut out a hole, see image on how Ford does it. Repeat for other post. They are 12 cm apart on center.
From top, Push black tube in, it is keyed and I believe they are RL specifc. Push in until it clicks, may need to lightly tap. Test fit post.
The front head rests are spaced 15 mm, so they dont fit. I found a set from an unusal ZX3 with them. Maybe ones from a Windstar or Explorer rears will fit?