I've never made one but looking at what i can find on the Prosaro ingredients list and having made moisturisers you'll need an oil part and a water part and an emulsifier to combine them.
For the oil part i'd include some castor oil as it's hydroscopic so will help to retain moisture, i'd also include a good portion of vegetable glycerine for the same reason. For the emulsifier i'd use Emulsifying wax BP as it's very easy to use. I imagine you wouldn't want it to thick so that it absorbs quickly.
I'd try some thing like this:
Sweet almond oil 15%
Castor oil 10%
Emulsifying wax BP 3%
Glycerine 15%
Water 54%
Vitamin E oil 1% (prevents the oils going rancid)
Preservative 1% (prevents bacteria, yeasts and moulds)
Essential oils of choice 1%
To make it melt the oils and wax in a small bowl then add to the warmed water/glycerine solution (i put both in a double boiler/ban marie to melt and warm up) mix it well then allow to cool mixing regularly. when it starts to thicken add the Vit E/E.O./preservative and mix well.
The water portion can be infused with what ever you want, flowers, herbs, teas oats etc.
Emulsifying wax BP usage range is 2-6% so feel free to experiment, more = thicker.
The Soap Kitchen is a good resource for ingredients.