I have tried it with a sulfate shampoo and used it 50/50. Most people have success with that ratio, some more or less depending on the shampoo used. I've also heard of people adding water to their mix. I say do whatever works. I'm waiting on a new shampoo that is sulfate free and should be more gentle, so I won't start out with a 50/50 mix. I usually mix it up in a two oz bottle, so I will probably fill the bottle 1/3 with coconut oil and the rest with the shampoo. I'm also going to try using babassu oil to see which I like better. It was another oil recommended for this method.
I've read that you will get better results by using a shampoo with very simple ingredients, otherwise you may have problems with build up. Last time I used a shampoo bar with awesome results. I slathered my hair with coconut oil and then washed with the shampoo bar. That may not work for everyone. I've also tried out non CG shampoos with sulfates, Garnier fructis pure clean and Aussie moist shampoo, which can be drying if used too often. I mix it in a 2 oz bottle which lasts a few washes for me.
I washed with the oil shampoo on Saturday and have co-washed twice since then. I think it's time to use the oil shampoo mix again.
What shampoo did you use?