Benzoic acid is present in nature…Its found in many fruits like strawberry cranberry, , plums etc.
I noticed that you had so much apprehension about food ingredients.
I remember you worry about invert sugar and glycerin when they
exist in nature.
I suggest you read more about those materials so you can understand more as well as how to use it properly…
There are many antifungal material but I would rather suggest that you familiarize through your own effort.
Things like benzoates, sorbates, propionates, acetates/ diacetates, etc
Ingredients application shoukd start with familiarity so it can ensure confidence in its use…
You should also understand the concept of water activity and hurdle preservation as that is applicable in your product.