What kind is right for my fine short hair?

I need help.  I live in the NY/NJ/CT metro area and I have short 3-4 and 5 inch fine thin hair that I am trying to grow.  I always get to this point and get it cut again because I hate the way it looks.  I am looking to you all for help and advice as well as salon suggestions.  In other words what type of extension and where can I go???  Thanks so much