That's good that you avoid using flat iron hair straighteners. No matter how much the advertise about their latest technology of the ceramic plates "that will not damage" you hair, it is still exposed to heat and will dry them up. I have thick hair also and instead of using the iron, I use the blow dryer with cool heat. Before I do that, I wrap my wet hair into a towel for about 15-20 minutes until it is half dried. Then, I take like a anti frizz serum (like biosilk, dime size amount) and rub it into my hair with my fingers and blow dry it, pointing the dryer straight down (instead of the position where would hold it like a gun). I would blow dry it until it is done. If you have a lot of hair, you can blow dry half of the bottom hair first (your top half should be clipped up), and then blow dry the top half afterwards. And then I go to sleep so that it is laid on so that the next morning it won't be frizzy.
OR you could go to the salon and have your hair straightened with the japanese method. They usually put like a chemical in your hair. This treatment will costs you about $70-$200, depending the quality of it and stuff like that. My friend has has her done for $150, and it turns out really nice. She was scared to go swimming out in public because her hair would get frizzy afterwards, but now she feels a lot better. If you do this method, you hair will come out as if you used a flat iron even if you just let you hair stay wet and not dry it. Anyways, sorry too wordy =)
had the same problemo.