We purchased our rig with no factory mattress, opting instead to put the credit towards a good quality queen mattress. Not sure why we decided not to install the Sleep Number we had on the farm, but we went with a name brand that suited us. I recall it was somewhat of a challenge to get the queen up and into the bedroom, not sure if we could have made it with a king size.
Regarding the Sleep Number bed....I have learned that their "pro-rated" warranty leaves a little to be desired...our pump failed, and if I recall correctly, a replacement was going to run over $500. The bed is now in the guest bdrm at our daughters home, and we just use a small, standard air compressor to fill the bed to the desired comfort level when needed.
Regards
Gemstone