"they" make anything if you are willing to pay! Foretravel, Newell, Entegra, and maybe even Tiffin. But you will have a tough time staying under that 26,000 weight limit you have imposed on yourself.
And I think your biggest problem will be finding a true king size mattress in a coach. Most will likely have RV sized king mattress. Easier to find a true queen size mattress, even my 1994 Foretravel has that. But there are many coaches out there that do not have full sized queen mattresses! Many have cut down queen sized mattresses.