Everyone who makes soap knows that castor is just one of those wonderful oils that makes handmade soap lather like crazy. I personally wouldn't omit castor from my soaps because I really think it adds something special to each bar.
There is some confusion though as castor oil is often used to super-fat soap. This means that it is ususally added at trace... this useage however doesn't add to the lathering ability of your soap. You MUST add the castor oil to your pot before adding in your lye liquid, so that the castor oil will become fully saponified in order to produce that desired extra lathering quality! And no need to cut back on your coconut oil/ PKO as these are typically the main lather creators... castor will simply enhance that lather & bring it to a new lather as well as condition. Happy soaping!