I read the OP and suddenly felt like a kid in a classroom who had the answer:
"I know! Ooo! Ooo! Pick me! C'mon!"
About a month ago, I did some research on a similar topic. I became curious about making my own plant-based shampoo. I dug into what made soap berries... soapy. Plant-based surfactants like those found in soap berries are known as saponins. This led to a deep and twisty rabbit hole of research.
I remember reading about alfalfa, which contains a significant portion of saponins. Per the chart in the link below, Alfalfa's saponin content is similar to soapwort's. Adding it to CP soap could theoretically increase foaming and detergency. YMMV as I don't know the exact pH range at which alfalfa saponins are active as surfactants.
If I had it on-hand, I would totally experiment with it. I'm not familiar with any particular extraction process for saponins but if ever in doubt, make tea.
I would brew up an extra strong batch of alfalfa tea with a long and low temp steep around 122F (50C) in distilled water. I would then replace the recipe water with the tea to see if it made any difference. You could also try it in powder form to see if that works also.
https://www.intechopen.com/books/ap...iological-active-surfactants-from-plants#tab1
Despite all the interesting research, I decided to go with Coco-glucoside to save myself time.