Hot air rushing out the top of your house is being replaced by cold air sucked in at the bottom of your house.
- This is called the "Stack Effect."
- Do a search and you will find a lot of nice illustrations of Stack Effect.
You need to stop the flow of cold air
Typical insulation may slow the airflow a little but it doesn't stop it. Imagine wearing a loose knit sweater on a 5 degree windy day. Now imagine putting a windbreaker over the sweater. Air leakage makes typical insulation ineffective.
What you need is to stop the cold air coming in low in your house which prevents the floor from ever warming up.
Spray foam is a common solution
A common solution is to spray foam your basement rim joist (box band, sill plate, etc...). Spray foam air seals as well as insulates. Often the foam is brought down the walls for its insulation value.
See if your state has a Home Performance program.
- They will come out and help you measure and quantify your problems both before AND after repairs. This is important.
- Many air leaks are invisible.
- You need before and after measurements of leakage or you don't know if anything was accomplished.