A couple of strait perm questions.?

I am completly fed up with my severly curly hair. It like makes an Afro sometimes so I am thinking of getting a straight perm. I want to know how straight it'll come out. When I straighten my hair with an expensive chi one it comes out really hard and it's like chunky. I want to know if it comes out silky smooth and really straight and looks natural. Are there anything I can't do or use on my hair? And yes, I'm getting it professionaly done. Thanks in advance. :)