I use a double boiler to melt a whole bunch of different things together for coating boots, knife sheaths, knives, etc...possible ingredients include:
1. The wax used in cheap ($1-$2) toilet gasket rings ... this is a greasy, soft, sticky wax containing (I believe) beeswax ... good stuff.
2. Coconut oil
3. Petrolatum (vaseline)
4. Paraffin wax
5. USP Mineral Oil (sold as a laxative)
6. Kerosene as a thinner/vehicle
For a "summer mixture" I err on the side of the more-solid ingredients such as paraffin and beeswax; for a "winter mixture" I err on the side of the more liquid ingredients such as mineral oil and coconut oil...
To fight mold, I will sometimes (before waterproofing) apply a strong solution of borax and water to the leather, then let it dry, then apply the oil/wax/waterproofing material.
If I have any trouble getting the stuff to sink in/absorb into the leather, I will judiciously use a heat gun, but you have to be real careful around stitch lines and seams with a heat gun...