I’m not very knowledgeable about essential oils. I have used lavender, clary sage, geranium and sweet patchouli in a blend for a facial soap. I was quite happy with it but what works for one person doesn’t necessarily work for someone else. Also, I didn’t choose all of these just for dryness. I was also interested in toning, etc. Of course, now I mainly use essential oils in leave-on products since I think they’re a little expensive to add to something which is only going to be on my skin for a few minutes. JMO
If you really want to use an EO, then I’d recommend lavender because it’s kind of an all purpose oil and is one of the safest to use.
Here are a few sites which you might find helpful for more info on essential oils.
http://www.aromaweb.com/default.asp
http://www.essentialoils.co.za/index.htm
http://www.naturesgift.com/essentialoil-skincare.htm
A simple recipe you could try
75% olive oil
25% coconut oil
I’d leave out the canola since many people have mentioned it has a short shelf life and can go rancid in soap. You also want to use a water discount with high percentage olive oil soap so it won’t take as long to set up. I don’t know how experienced you are so I’d suggest using 33% lye concentration. This will give you a little more time until trace but not so long that you’ll get frustrated.
As for rebatching your recipe, I’m not sure what to recommend since you really don’t know how much lye you used. You could chop your soap up (I’d recommend shredding it for easier incorporation of oil), heat in a double boiler and add another 2 oz – 3 oz of olive oil. That might be enough if you didn’t add more than 3.8 or 3.9 oz of lye. But I don’t know for sure.
Superfat/lye discount just means using more oil or less lye that what is needed for 100% saponification. I tend to use the terms interchangeably but really what I use is a lye discount since I calculate my recipes with less lye. Superfat is adding extra oil which is what you’ll be doing when you rebatch.