...inflatable mattresses...
.
a)
Unless your van interior temperature is perfectly stable, air inside the mattress shrinks as it cools...
... leading to sags.
.
In cool weather, I like a little heat.
That would expand the air inside the mattress...
...turning it egg-shape.
.
.
A cheap alternative (while potentially helping involuntary vehicle-dwellers):
Saint Vincent de Paul acquires used mattress donations, strips the textile exterior right down to the springs, then re-builds them with new material.
Would I?
Probably not.
Nor would I hang a hammock.
.
.
b)
My tirade against foam:
Unless you are proactive about humidity inside your rig -- Open! The! Windows! -- foam loves moisturizing.
A moist bed eagerly invites fungus.
.
Horror stories abound about lifting the mattress...
... and discovering pools of water, the mattress reeking and returning to its base elements with the assistance of black mold.
.
For our ExpeditionVehicle, I fabricated our bed platform using expanded metal, similar to stout window-screen.
This allows plenty of ventilation under the mattress.
.
And 'yes', our mattress is identical to any mattress in a stand-still house.
.
.
[edited to add (because I 'sometimes' get carried away)]
c)
We started our interior with our essentials:
1) our bunk, then
2) added our galley and head.
Everything else is just fluff for fun.