I generally use SFIC soap base. I have used oatmeal, honey, powdered milks (which happens to be my favorite), vitamin E, herbs, all kinds of exfoliants, etc... Adding oils and/or butters in small quantities makes a very slick and softer bar with practically no lather. Perhaps the base that you are using can handle such a change. I have also added some olive oil and had ZERO lather. LOL! I think that SFIC base is perfect as is. I do love the dry milks in some of my variatations. Did you really add lotion to your MP base? That sounds so interesting and I always pondered doing that, but did your finished soaps get a lot softer?