I have had naturally curly frizzy hair my whole life. I have tried getting my hair straightened but as another poster noted unless you flat iron it, you still get frizzy straight hair.
I found a product called Brazilian Keratin for $43 on ebay. My husband followed the YouTube instructions. It was a 3 hour process for him to do it but the results are unbelievable ..... it got rid of all my frizz. It used to take me an hour to blow dry my hair and 30 minutes to flat iron. Now it takes me 10 minutes to blow dry and 10 minutes to flat iron. Today I didn't even flat iron my hair and my hair looks great. It took a tighter curl and made it a bit looser but no frizz. I did the process a month ago and everyone compliments me. I am 40 and everyone tells me I look like a college kid. I even got carded last week. Also, before I used to use a ton of gel in my hair. Now, I don't even have to condition my hair, it is just so shiny. Seriously it is the best product ever made for people who have frizzy hair. I went to my hairdresser yesterday and she was in disbelief on how much a difference it made. The product says it will last 3-4 months. I will be a repeat customer. Good Luck.