Check out the one piece "Spine Fin Coil" technology offered by Trane & American Standard.
My house did not have A/C when I bought it. The fire box on the original furnace was severely corroded from having no cap on the exhaust vent pipe. Rain came down the pipe into the unit.
Replaced the furnace with an American Standard 80% efficient 2-stage unit, a 4" thick HEPA filter, programable thermostat & added the American Standard A/C. At the time ( about 6-7 years ago) the 80% furnaces were more reliable & longer lasting than the 90+% units. Don't know how well they fare these days.
My heating bill dropped substantially & the house is more comfortable. The A/C rocks & will often be a bit too chilly.