Any of the leather conditioners will work plenty fine, though I'd stay away from the mineral oil as its too easy to over do it.
I'm a "use what ya got" kind of fellow, Sno Seal is what your familiar with. Start slow with thin coats and allow it to fully soak in before starting the next. Two good coats should get the sheath back to flexible and not floppy. As long as there are no cracks in the leather you should be good to go. If your wanting the process to go a little quicker sit the coated sheath in a sunny window till you see no more wet spots.