I just wanted to say that I think you've made the right decision in sticking with waterbased markers. They're the closest thing to using an ink pad and blender pen, they're less expensive than Copics, and they don't contain solvents like Copics do, so you don't have to worry about what you're inhaling. Who knows what harm the solvents in those pens can do to a person over time???
I use Tombows myself and I don't know of another company that makes waterbased markers with the range of colours that Tombow has. If I don't have the exact shade I need, I make it myself by combining the ink from a couple Tombow markers, or I get out my watercolour paints and do the same thing... mix colours until I get the shade I want.
There's a lady by the name of Krista Schneider who uses Tombows for watercolouring and her work is amazing. My local stamp store used to sell her step-by-step workbook, called Simple Watercolor Projects, demonstrating how to colour using Tombows and there are blank pages for you to practice on.
She has her own stamp line called Sunshine Designs...
She also has a new website that is still under construction. Perhaps when it's finished, there will be some of her artwork on there for you to see, that was done with Tombow markers.
Hope this helps a little!