You're probably over thinking it a bit. WD-40 works fine enough for many users on the forums here. A lot of people don't even lube the pivot, since the oil can attract lint and dirt from being carried around. Especially since most design of folding knives have a pivot washer made of teflon or phosphor bronze, which are somewhat considered "self lubricating".
Personally I'll use whatever quality oil I have laying around that won't go rancid. Especially mineral oil which is easy to find in local stores and is considered non toxic. Another popular option is to use a oil that dries and leaves a "waxy" film that won't attract dirt, such as Sentry Solutions Tuf-Glide or Eezox.
