Teach Soap

I've been thinking of adding some GM to bath truffles.
My usual recepie calls for 2:1 (Baking Soda vs Citric Acid), some Shea Butter, Cocoa Butter and Olive Oil, EO/FO and colour. To this I am planning to add some Polysorbate 80 and a part of powdered Goats Milk. None of them I used before. Should I change the 2:1 ratio due to GM? Maybe decrease some BS or just add a small part of GM? Should I add some preservative (because of GM)? And if yes, which one would you recommend to be the mildest but efective for this kind of products?
Each Bath Truffle is meant to be used for one bath as they are pretty small but they are supposed to be packed a few in one bag - later when I am ready to sell (which will take quite some time to experiment first).
I noticed somewhere that polysorbate 80 should be used as much as EO/FO for the purpose of dispersing the oils evenly. Would that be ok?
Any recommendation would be higly appreciated...