The first thing to do would be to find out if there is any insulation in the walls. 37 years old is not really old - My house was built in 1965 and has insulated walls but it has drywall also. If there is no insulation and your plaster is in good shape there is a couple of alternatives to look into. There is the rock wool or celulose blow in products. These work good. I've heard complaints that it settles after awhile but a couple old houses I helped remodel it was still right to the top of the walls. Then there is the slow expanding foam. I have never seen it used myself but they did use it on This Old House and it looked like a good deal. I think I would lean toward the foam as the best choice. You only have to make small holes and you get a good R value - probably better than fiberglass.