According to the CMHC ( Canada Mortgage and Housing Corporation), adding insulation to attics is the most cost effective.
Blown in cellulose fibre is an effective solution to add or upgrade your attic insulation and can reduce your heating and cooling costs
If your attic is not properly insulated, it can greatly reduce the energy efficiency of your home.
All that work getting your rooms toasty warm is literally going out the roof, both your heat and your energy costs.