@raynbow- I think that if you blow dry your hair the right way, you can make it appear straight without too much damage. It is definitely better than using harsh chemicals that make your hair very dry and brittle.
First of all, you will need to wash and rinse your hair. Since you said that using too many hair products makes your hair look oily, make sure that you rinse it thoroughly after using shampoo and conditioner.
Next, remove excess water from your hair with a fluffy bath towel. This will decrease the amount of time you will have to spend using your hair dryer.
Finally, once you start using your hair dryer, put it on a low heat setting. Continue blow drying and straightening your hair by using a fine-toothed comb as you dry it. Once dry, simply spritz your hair with hair spray to keep its new, straight appearance in place.