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. Med porosity. Med thickness. Med density.

Low-poo: Shea Moisture Coconut & Hibiscus
Conditioner/co-wash: Jason Moisturising Aloe Vera

Leave-in: Aunt Jackie's Curls & Coils Quench Moisture Intensive
Refreshing: TRESemmé Naturals Nourishing Moisture Aloe Vera & Avocado
Gel: Ouidad Climate Control Heat & Humidity
Treatments: Once a week, alternate between Coconut Milk and Coconut Oil before washing

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