You need somebody to figure out if a new "upper" can work with your "lower." Remember what I mentioned before. Most of these A/C units now seem to be sold as Upper (Rooftop, Compressor, Coils, etc.) and Lower.
That needs figured out before you do any shopping. My Guess, and it's only a Guess, that a Ducted system like yours requires a different Upper than the kind you mentioned. The Ductless one on sale, controls on the unit.
I can only suppose there could be thermostat/control issues too. If you could get an upper to match existing lower, and only needed a different thermostat, wouldn't that be a good fix?
