How to have straight hair without heat?

Don't get your hair relaxed, that will damage your hair even more. One method I know you can use on synthetic wigs to straighten the fibers is to pour hot water (not boiling, but pretty hot) over the hair and let it dry naturally. You could lay down with your hair hanging away from your scalp and have somebody help you to pour the water over. This won't damage your hair, because you can safely use it on wig fibers that would be otherwise destroyed by heat. I've never done this on real hair, but I think it would probably work.