Regardless of what type of foundation you decide on, always tamp the soil on the your foundation trench to compress the soil and minimize future movement.
A simple tamper can be made from a heavy piece of a tree (4 or 5 inches across). Either drill a hole and stick a dowel or pipe through the hole to make a handle, or chop a handgrip with a hatchet. Another option is to screw a piece of plywood (1 foot square + or -) onto the bottom of your tamper. The tampers can have bells or bottle caps nailed loosely to add some percussion to the tamping rhythm. (A 'tamporine'.) Another simple tamper can be made out of a 2 1/2 inch (plus or minus) metal pipe filled with packed dirt or stones and capped on the ends. You can use the special caps they make for the tops of fences. The metal pipe can have a flat piece of steel (1 foot square, + or -) welded onto the bottom. The smaller the bottom of the tamper, the more pounds per square inch you'll get out of it.
Tamping is hard work. Do a little at a time and pass it on to the next person. Remember to keep your knees bent, the tamper close to your body, and breathe a lot. To save effort, lift the tamper and let gravity do the tamping. Even though you might not be able to see the results, this is a very important step and will do a lot towards stabilizing the ground under the house.
Always tamp the ground before building onto it.