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: Shea Moisture Coconut & Hibiscus
Co-wash & conditioner: Jason Moisturising Aloe Vera

Leave-in & refresher: Aunt Jackie's Curls & Coils Quench Moisture Intensive
Gel: Ouidad Climate Control Heat & Humidity
Treatments: Coconut Milk before washing, once every 2 weeks, followed by an ACV rinse

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