I don't think coco is your answer. Try sand, or a greater amount of perlite, to reduce retention and improve porosity (GrowStones Soil Aeration mix comes to mind as well). Coco produces great yields when used hydroponically, but as an organic medium I find it to be no better or worse than what you have now. I don't think adding coco to your mix is a bad idea, far from that! But I would not expect it's addition alone to increase your yields.