2 years ago I purchased a home that needed some repair. The home is/was extremely cold and drafty. I thought it was only due to 20 year old oil furnace. Since I know a furnace contractor, he replaced my furnace with a gas furnace at a very good price, which did lower my utility bills, however, the house is still drafty. I realized that there is only 3-4" of blown fiberglass insulation in the attic. From what I've read, for my area (North Central PA), I need somewhere between 16 and 20" of insulation. Which is the most cost effective material to use for a house that is 65 years old and I don't plan on being in for more than 5 years. Also, the previous owners built an addition to the back of the home, which connects to the garage. The addition has a cathedral ceiling, which is about 18feet at its highest peak. On the other side if the wall is the garage. I am debating on whether to use spray foam for that wall, since it is not adequately insulated (only about 7feet of the wall is insulated. This is the room that gets most used in the house and it gets cold in the winter and hot in the summer. I plan on hiring a contractor for both jobs since I'm not at all handy. Any tips or suggestions are appreciated. Thank you.

The extreme ceiling height in that room probably has much to do with the discomfort, especially in winter because you're heating all that unoccupied space up there, and the heat rising to that space causes cool air to be drawn in from any of several possible sources, thus possibly creating the drafts you feel.

Much also depends on how the space is heated and cooled: location of grilles and diffusers, air temperatures and velocities. lots of factors, even the location of thermostats.

Attic insulation is vital, and the goal should be to get as much up there as you possibly can fit and afford. Then, spend some time and money making certain that the house is well-sealed by caulking and sealing around all windows and doors, installing storm windows whereever there is single-glazed windows, and paying close attention to things like electrical outlets in exterior walls as a source of drafts.

If you have access in the basement or crawl space, as the case may be, be sure the floor above is insulated, and that there is insulation along the rim joists, and be sure that any vapor retarder is UP against the subfloor and not visible in the space below. Experienced insulation installers often get this wrong.