We upgraded ours to a residential Qn through Denver Mattress while up in Erie, PA . We opted for the Durango because of the height, but there were others that would have worked as well. It has individually wrapped coils unlike the Doctor's Choice we orginally went to buy.
I noticed last week there's a Denver Mattress store in Charlotte, NC when I was pricing a new pillow. Found they now also carry RV mattress sizes. RV Short Qn 60x75 and RV King 72x80.
http://denvermattress.furniturerow.com/dmc/