I really love the fact that you are trying out every method, this is how you tend to find a medium that suits you perfectly. Improving on your sketch will help you a lot, sketching is one of the first step to a successful drawing. I also think there will be a watercolor base paper out there that can help but finding it is another thing.

What type of pen do you use?? have you tried using hot water to heat the ink tube in the pen?