Just MHO, but I'm guessing that you may not notice a difference is you are substituting as opposed to developing an entirely new recipe. With that said, an article from the National Center for Biotechnology Information (
Commercially available alternatives to palm oil) has some interesting alternatives
I think that that is pretty SOP for the majority of soap makers. When I first started out, I had collected a boat load of different recipes, but it's not very cost effective to have 20 different oils and butters on hand. I started with a basic recipe of Olive, Coconut, Palm and Castor Oils (BrambleBerry's Beginning Soap Recipe). When it came time to order more supplies...I bought a dozen different oils and butters...substituting between 5% to 20%. In a discussion about the real-life benefits of using various oils and butters, I was told that with the exception of Castor Oil, adding less than 10% of any ingredient was a waste of money. Adding expensive ingredients of any amount was also a waste of money as the majority of any 'benefit' would 1) be destroyed by the Lye and 2) soap is a wash on/rinse off product and thus not on the skin long enough. In short, save the good stuff for leave on products like lotions.
I can't speak to beer, AVJ, Tussah Silk and a bunch of other additives, but I can with Goat Milk, Kaolin Clay and Sodium Lactate. I don't know if Goat Milk is "better" for the skin that soap make with Distilled Water...again, it's a wash on/rinse off product, but I can tell the difference between a bar of GMS and a bar of Regular Soap and that is less about it being "Goat" milk and probably just milk in general with its added fat and sugars. I could probably get the same 'feel' if I increased my SuperFat and add sugar or honey. And Lord knows it would be less of a hassle since I use fresh goat milk as opposed to powdered, but I enjoy the process...it's very zen...kind of like when I wind hanks of yarn into cakes.
With regard to the KC...some say it provides more 'slip', some say it helps to 'anchor' FOs...I don't know, it's soap, it's naturally 'slippery'. LOL As to the anchoring...the jury is still out on that one. I haven't tested it...maybe I'll do that this weekend. Make a small batch for my round cavity molds...add KO to one and not the other and put the soap on the shelf and check on it over the next year.
Last is the Sodium Lactate...I do find that it makes it a bit easier to unmold a lot of my soaps...especially during the Fall/Winter when it gets cold and damp. I could probably make my own or grab the salt shaker, but it's cheap enough and a gallon of the stuff lasts a long time.
To be honest, I don't get a lot of the additives I see folks putting into their soaps on YouTube...to me it's just more crap to buy, more crap to store, more crap to list on my label. Watched one gal add about a dozen different 'additives' and I kept thinking...is there any more for oils?
But the nice thing about making your own soap, it that you can experiment with stuff like that. A half ounce of Tussah Silk is $2.98 at BB, an ounce of Collodial Oatmeal is a buck and a quarter, an ounce of KO is a buck, seventy-five and so on and so forth.