Help/Advice for green hair care? Please see details.

Although I recently was “no-poo” (that is, I only washed my hair with baking soda/water and vinegar/water), I found that my hair built up some sort of residue over time, especially on the back of my head (not the roots).

I did some research and eventually switched to a sea-salt based shampoo, but in the interim, I used a store bought shampoo with all the nasty ‘cones and SLS and whatnot. While I was using the store-bought, my hair was fine—no build-up, easy to manage, shiny, etc.

However, after I switched to the sea-salt shampoo, and a few showers, my hair began to develop that same residue again.
Vinegar rinses don’t work for this problem (I tried).

Any advice? Am I doomed to using commercial shampoos? If so, can you recommend some good, all-natural, free of nasty things shampoo that smells good and isn’t hideously expensive?

(I don’t use product or conditioner in my very thick, naturally somewhat-oily hair.)