I've always read that vinegar is a natural fabric softener.
I found a few "recipes" for homemade fabric softener and this was the easiest!
1 cup baking soda
1 Gallon of white vinegar
30 drops of essential oil
(If using peppermint, use 15 drops)
Here's what you do:
Mix all ingredients (There will be a bubbly reaction)
Shake well before every use and use about 1/2 cup per load!
For larger batches, you can use 1 cup