What's worse? Using the semi-toxic (really?) mattress the RV came with, or throwing it out and replacing it with a non-toxic (really?) mattress? In either case, the first mattress was still manufactured and put into the environment. In the second case, that first mattress was wasted, and ANOTHER was also manufactured. Seems to me, one is "greener" in this case if one uses the mattress the trailer came with.
Just as one doesn't save money by buying something ("buy now and save!"), one doesn't reduce consumption and footprint by replacing items that get the job done.
There is a point where comfort enters into the equation, but if one's primary concern is reducing consumption and environmental footprint - see above.