ISO: bread gets moldy

My home made bread usually gets moldy before two of us can eat it all. What mild preservative can I add to the various recipies that I may use, and that would preserve the bread until the whole loaf, or most of it, can be eaten, instead of just 60% of it?
I seem to recall that bakeries used to add a small percentage of some mild ingredient to preserve freshness, but not sure what that was. Perhaps "Benzoate of soda" or something that sounds like that.