^ you can use a straightening iron every day if you want to, you just have to take good care of your hair before, during and after straightening it. Using treatment serums and thermal shield sprays stops your hair from being damaged, and letting your hair cool before straightening a section again stops your hair from burning and works better than on hot hair.
(salon rant)
Also, always buy salon stuff. Things from supermarkets, department stores, etc are very generic and tend to be not as good for your hair. You are also self-diagnosing and treating any hair problems you have, which can make things worse. It's like comparing supermarket ough mixture to the pharmacy only stuff. The latter is better formulated, has better ingredients and is often recommended for your specific situation.
Finally, get a good straightener. Here i have to be popularist and recommend a ghd. I have had one for 3 years now and it is perfect. In the meantime, my friend has gone through countless, cheaper ones and they constantly break, burn her hair and don't give as good results. In the end, it is better for your hip pocket and your hair to buy the best.
Yeah, massive rant here. And I know what I am talking about- my mum and aunt are hairdressers and own a salon together that I regularly work in. I use a straightening iron every day (my hair is naurally a weird cross between straight and curly) and colour it frequently (again, professional job and products!!!!), and I have the thickest, healthiest hair of anybody I know. It is one of my favourite things about me- I love it