The trim piece on our beds is only about 3/4" to 1" tall. I cut a datto in the boards that slip over the trim piece on each side. Keeping the boards (2 boards about 3' long and 3" wider than the aisle) in place. The center of the bed where the boards are over the aisle is about 3/4"-1" higher; we usually throw a couple of old blankets over the wood and sharp edges so that the air mattress isn't punctured by anything sharp. With the air mattress you don't feel any difference in the height.
If the 3" high edges are strong enough to support your weight and that of the boards and you have foam pads on the beds now; I would leave the foam pads in place, put the boards across the aisle, throw an old blanket across the whole thing and put the air mattress on top.
With the aisle way blocked by the bed it means climbing out of bed to get to the head or into the galley. But it's worth it to me to sleep next to my wife and be in a bed that is more than 48" wide. And since the whole berthing area becomes a bed, you can sleep with your head in any direction that is comfortable.