How does it handle as-is? If it handles OK, I would not worry too much.
It matters a lot where the weight is located. The lighter (air)mattress will make the front axle lighter, not so much the rear. For a simple test, you could remove the mattress altogether and see how it affects the ride quality.
I suppose you want to get rid of the rear axle weight first, so any weight removed behind the axle / camper c.o.g. is more effective. And the further up the weight is, the more noticeable it will probably be w.r.t handling.
From personal experience: I have removed the A/C from our old Lance 915 on our Silverado 2500HD. The difference in sway was very much noticeable right away.