Matress (how thick?)

I am in the process of looking for a used Trailmanor. My question is how thick of a mattress can you install. I want to install a new Tempur-Pedic style foam mattress in whatever unit I buy. At this point I dont know what model number unit I will buy. It the used Trailmanor market you jump when you find a clean one at a good price. Also I guess I could use words of wisdon on what is the bedding like that comes from the factory. Our plan is to take a 6 to 8 week trip around the country next summer (retirement party )