Immediately: Turn the thermostat down to 60 or 62 for 8 hours at night, turn down another 6 hours if you leave during the day. Wear socks & slippers & house hoodie around the house & stay busy. Then 66 is warm enough. A heated mattress pad makes you toasty in a cool room. Next: Research hvac contractors & rebates & system choices. Don’t be in too much of a hurry to cut your bills this winter with a new heating system. It could be far more expensive long term to make a hasty decision with the wrong outfit