The AC you have now is a ducted AC. The 2nd one you want will be a non ducted.
https://www.rvpartscountry.com/Dometic13500DuoThermBrisk2TopUnitOnlyAirConditioner.html?gclid=Cj0KCQjwvo_qBRDQARIsAE-bsH_y6y8TO27fRqzIbbX67wOiIEg6pu0zWMxjeR7wj9RmNfMRfSoy-DwaAvexEALw_wcB . It would be installed in place of the roof vent in the bedroom.When you decide on AC you want don't forget to get the inside air box too it's extra.
https://www.rvpartscountry.com/Dometic13500DuoThermBrisk2TopUnitOnlyAirConditioner.html?gclid=Cj0KCQjwvo_qBRDQARIsAE-bsH_y6y8TO27fRqzIbbX67wOiIEg6pu0zWMxjeR7wj9RmNfMRfSoy-DwaAvexEALw_wcB The installation requires going on roof with new AC. This is best done with 2 or more people. The 120v wiring should be in the ceiling at the vent. That's what they mean by prewired. The are numerous you-tube videos on installing a 2nd AC. I'd watch several and then decide if it's something you could do.
https://www.youtube.com/watch?v=4O6CCIcehbQ