Hair Extension

I hate having medium-length hair! I just never feel right about it. Don't you have the feeling that the back of your hair is 'waving out' for some reasons that it can never be fixed, even though you already flat-ironed them? I have that feeling every day in the morning that I am desperately wanting hair extensions at the moment. I wanna have a long and 'au-naturel' looking wavy hair like them. 

What do you think? Do I need hair extension? How much do you think it is? Anybody has done that before? Please, I need some input! My hair is unbelievably difficult to manage!

xoxo