other is check the air flow in your attic. A Solar Guard Blanket can be attached to the rafters that will reflect the radiant heat from the house back down into the house. It also keeps the heat from the roof from getting during the summers. Primarily used as a product in metal roofing installations. You can also foam all accessible plywood seams with a foam gun they only cost about $60.00 and $5 for cans of foam. This will prevent airflow movement through the plywood which contributes to outside heat loss more than you realize. Your situation sounds like you have ventilation issues where the heat is moving to the higher cealings or second story. You could also look a high efficiency ductless system for the rooms with 22 SEER or greater rating.

Insulation is expensive and dictated by code. In the Charlotte region, attic insulation code is 30 but I had 36 installed for more money and calculated the payback was 5 years. NOVA probably has a 36 rating. But it will take a while to get your money back.