For me it depends on the leather. Garment leather I treat differently than saddle leather. If you're using neatsfoot oil then it's likely saddle leather.
For saddle leather, it now depends on the function of the item...laffs. For harnesses, outdoor belts & such exposed to the weather regularily, the best thing I've found is Cocoline. I've seen English harnesses over 150 years old in perfect condition that were always treated with it. It's been around awhile. It will darken the leather some however & acts as a waterproof.
As Pat says, do not use a silicon product as it does not really penetrate but remains on the surface not allowing the leather to "breathe" properly. In a damp climate siliconed leather will rot, in a dry climate it will harden & crack.
For a home made type thing you can just add waxes to pure neatsfoot, or mink, or other similar oil with a little heat. The more wax you use, the greater the sheen. Some waxes produce a higher sheen than others, thought difficult to see any difference after a time really. The neatsfoot oil I get doesn't have any silicon, must cost a penny more so we don't get it up here in Canada....LOL.