Soap to keep an ocean clean?

If what you said about soap always having to contain amphiphilic molecules then I would say there isn't much you can do. I do not know much about soap at all except that it helps clean your hands/body, so here is my advice. Use as little as possible. I am doubting that you are going to find a perfect, environmentally safe soap, so just limit yourself with the soap you already use. That's all I can say.