You've got a few options:
Neatsfoot oil, apply very lightly and let it soak in well. If you overdo it the leather will get floppy.
Leather conditioners like Sno Seal, Aussie Leather Conditioner, and a few others that are oil and beeswax based.
Start with a dye that isnt alcohol based. Fiebings has a dye called Pro Oil Dye that in my experience does not harden the leather.