my house is hot and cold

Seattle is certainly more temperate than most places in the world. Most of the winter the high is 45F, and rarely drops below 30F at night. The last few summers have been mostly highs around 80F. I can't think of a time when it went over 100F in the 10 years I've lived here, but it has probably happened at least once.

On hot days, my house gets pretty uncomfortable, and takes a long, long time to cool off. Part of the problem is that the upstairs only has 2 small windows, and they're on the north & south sides of the house, but the window mostly blows from the west.

There is a pretty good collection of tall pines around the house, and this summer I noticed something interesting. The pines keep the house in shade until about noon, and the house is quite comfortable until then. By 1pm, the house is hot. The sun stays steadily on the house until sunset. The room we tend to hang out in is on the south-west corner of the house, so we feel the heat.

When I can, I try to open the house in the evening, and close it up again the morning. Unforunately, the house gets very cold around 3-4am.

It seems like there should be some opportunities to make the house more comfortable in the summer, without turning on the heater in night, and without adding an air conditioner. If I plan carefully, I should be able to do it for very little money or other resources.

I could probably benefit by adding thermal mass and low awnings and improving insulation and airflow.

So now I need some information on how to improve these things in an existing house, for cheap.

Any favorites?