I change our64 Safari to a 13,500 BTU Dometic brand AC unit with a heat strip. It is fine for us. Heat pumps are not good in very cold conditions because is is a heat exchange type system. However we do not use the heat strip either. I also converted the Heater and water heater to a Precision Temp, Twin temp JR. system that does heating for the trailer plus instant and continuous hot water. That was the best conversion ever.
Sorry, I digress from the subject.
You could be surprised that it may not cost much to repair you old unit.
It could be as simple as replacing the start up capacitor.
Either way, here are a couple of things to look at.
Camping World has an internet sale on a low profile AC unit with heat strip.
Dometic Air Conditioners - Air Conditioners - Camping World
Here is a video on changing you start up capacitor.