OP, your hair is beautiful. Since you have such a loose wave/curl pattern I would definitely forgo a relaxer.
I am 3c mostly and I love QOD Organiq. Before you use keratin treatments I think you should try some of the keratin styling creams like Coppola Keratin Infusion or Keratin Express Daily Keratin.
I've heard that Design Essentials has a system that is not as harsh as a keratin treatment but it allows you to go between your natural texture and straight hair without altering your curl pattern.
Here's a video:Videos | Design Essentials