Old whip builders were notoriously innovative. The conditioner that has been passed down for generations in Australia is:
Equal parts of beef tallow, 30 weight motor oil and kerosene.
Personally, I have used pure neatsfoot for decades with excellent results. I have a saddle that is well over 70 years old and has been conditioned with pure neatsfoot exclusively.
In the more recent past, I have found that Pecards original conditioner is also an excellent choice.