The problem w/the numbers is that they don't really capture everything. They provide a pretty good starting point in a lot of instances, though. 30 % CO and 10% castor (assuming no goo) should make your bar pretty bubbly. But that much CO would be *way* too stripping for me. You can compensate by increasing the SF, but that reduces bubbles as well, and for me I still think it would not work. It is so dependent on what you need for your skin type that it is sort of a juggling act for a while.
So I stick w/my basic recipe, which is lower in the bubbly/cleansing oils, and then add stuff that seems to make good lather for me. Usually sugar, sodium lactate (for hardening, but I think improves lather), coconut milk (again, improves the feel of the lather for me but by increasing SF may decrease the amount of it), aloe, EDTA (I add this to deal w/soap scum, but I personally think it helps with lather as well.) You can see from all the parentheticals that there is some juggling in the poor overtaxed soapmaking brain!
ETA: If you want to experiment w/bubbly oils for your friend, they are pretty much the high cleansing ones like coconut, palm kernel oil (*not* palm oil), babassu. Plus castor.