Yes, heater core needs to be replaced, moisture on windshield with defrost is a sign of that, but could be a leak in the windshield's lower seal and dripping into core area, or A/C evaporator drain is plugged.
But smell of coolant means 100% heater core.
On my '94 Ranger the core was $28 and it took 20 minutes to replace, 4 screws and 2 hose clamps to remove and re-install.
You remove the heater core by removing it's lower cover under the glove box, 4 screws all facing down, remove the heater hoses, 2 clamps, put towel on floor board

, tilt and lower core out.
For the time being you can loop the heater hoses together, so no coolant is flowing in the cab, that should cut down on the fogging but not help with the cold
