But first problem you have to think about is your windows. Maybe you got, old, wooden ones? They are looking very cute, likely, but it is not enough. If you will exchange it for any modern, PCV pieces, you should have a chance to keep many of hot air inside of your rooms. You do not have to remove each piece at ones, you could do it in couple steps, to avoid too many expenditures in one week. Different relevant issue is your roof. When you will cover it with some fibreglass mesh, it could also keep your home a lot warmer in the time of winter, cause most of the air is escaping trough it, probably.
Then, you may invest some of cash in external wall insulation. It should be very giant cost, but it is worth it, more information here: insulation systems (insulation systems). Within couple years, costs of it will come back to you into the warming expenditures. Beside, when you wish, you could at the end prepare some interior insulation as well, using also fiberglass mesh – it is the best product for all this type of works. But where you may buy all the materials? It is very simple, go to the closest building store. You will find there all the stuff you require, from screwdrivers to fibreglass mesh.
When you are afraid of cold season, because of big costs of healing, there is a nice solution. You need to arrange an external wall insulation and exchange vintage windows with PCV ones, more: fibreglass mesh (fibreglass mesh). It should help you to spare a lot of money, and it is great for environment, because you should waste a lot less energy. And the best season to start renovation like this is summer. So maybe you may consider it?