It sounds as though you hair is already damaged, I would not recommend a permanent straightening if that is the case. I have known people with curly hair that had permanent straightening, and because the hair was already damaged her hair would dry out and break off. I think it is imperative that you have healthy hair before you consider doing such a thing. You really need to talk to a stylist about getting your hair back into shape before you do anything to it. There are a couple things I can recommmend to you, the first being vitamins, and the second being a thermal protector for when you straighten it. I do not straighten my hair (god did that for me), but I know Nioxin Bliss has been recommended here a couple times. The third thing I would recommend is regular haircuts until the damage is gone, so you don't damage any new growth. I copied this information from one of my previous posts and I hope it helps you.
You should consider taking a vitamin that contains the following:
Vitamin B-complex
Other B-vitamins (including folate, biotin and inositol)
Vitamin B-6
Vitamin C with bioflavonoids
Vitamin E
Beta-Carotene
The recommended daily dose of magnesium, sulfur, zinc
Flaxseed oil
These vitamins and minerals have been shown vital to keratin protein (you hair metabolism). Without them you hair growth can slow or stop, you can suffer hairloss, or your overall hair health can be compromised. Healthy hair starts from within the body. You should talk to your doctor about starting a vitamin regimen, and he/she can tell you how much your body/hair needs. Also get frequent hair cuts, because damaged hair could possibly damage any new growth.