How to have a healthier, straighter, hair?

Hi~! I have this enormous amount of hair... Every little strand is like a mini wire and I have a lot of it... It's like the end of the witches broom except softer. And it is also wavy. Its not straight or curly, its wavy making it poofy almost like an afro...It is only my top half including my bangs that is poofy and thick... the bottom half of my hair is actually normal and healthy... Why is that? My hair used to be normal but I think the wrong use of shampoo or too much heat has ruined it... I really want my old hair back. I'm Asian so I want that straight, long, shiny, beautiful, healthy hair. My hair is kind of course and whenever I separate or brush my hair out, it gets bigger and poofier. I used to straighten my hair every day with the use of a heat protector... but it always goes back to poofy after I wash it. So I stopped Ironing it. I'm really tired of ironing it every day. Is there a natural way I can get back my straighter hair? I also tried chemical straightening but It didn't make a difference except the loss of cash in my wallet... I heard something about REBONDING... Can that help my hair? What does it do? Please help me... For now, I don't iron my hair anymore and I just put biosilk... but that does not do anything... My hair is poofier and thicker than ever... Please, what can I do to make my hair straighter, thinner, and healthier at the same time? Thank you very much for your help :)