If I were you, I'd cut off as much of your damaged / thin ends as possible, so you're almost 'starting fresh'.

Then, if straight hair is really what you'd desire, I'd suggest you go and get a chemical straightening treatment done. It's a permanent thing (that obviously you'll need to get done again every 6 months - 1 year, as your roots come through) and would mean you don't have to straighten it every day.

Also, plenty of deep conditioning and coconut oil treatments will help moisture and 'patch' the damage on your hair.
3B. Medium porosity. Medium Thickness. High density.

Low-poo: SM Coconut & Hibiscus shampoo
Conditioner: Jason Moisturising Aloe Vera Conditioner

Leave-in: Baptism rinse
Styler: Ouidad Climate Control Heat & Humidity
Re-moisturising/refreshing: TRESemmé Naturals conditioner
Hot oil treatment: Organic Virgin Coconut Oil

UK curly. CG since October 2013.
Growing my hair out Rapunzel-style