Recipe #1
Combine honey, milk, salt and baking soda in a bowl. Fill your tub and pour the mixture in. Add the baby oil and a few drops of the fragrance.
Recipe #2:
OR, try this...
Turkey-red oil (a derivitave of
castor oil) acts as an emulsifying agent for other oils so
they won't coat your skin or the tub. Mix 3 parts turkey-red
oil to 1 part fragrance oil. Add a few drops to your bath.

Add a little of the mixture to your tub for a revitalizing bath. For bubbles, just add 1 cup of shampoo. For a nice scent, add a few drops of fragrance oil.

Mix the soap flakes, water and 2 tbsp glycerin in a pot and
set over low heat, stirring occasionally until the soap has
dissolved. (This liquid soap can be stored in a covered
container and used as an all-purpose soap or hand soap in the
kitchen.) In a bowl, add 2 cups of this mixture to the rest of
the glycerin, shampoo and add a few drops of your scented oil.
Put into a quart container and store covered at room
temperature. When you're ready to bathe, add about one cup to
your tub as it's filling.
Blend together all ingredients in blender. Add 1/2 cup of mixture to hot bath water.

Add herbs to your tub by either making an infusion of them How to make and use herb preparations and adding directly to the bath water, or putting the herbs into a muslin bag and tie it directly under the tap as the water is running. You can also add scented oil to the mixture if you want to. Here are a few ideas for herbs to use: