[jiroband]

I do not have experience with this; however, I found this resource for locating private label hair care product manufacturers:

http://www.cosmeticindex.com/private-label-hair-care.php

[jiroband]

First of all, be sure to include glycerin at around 3%. It’s an effective humectant and probably the least expensive one you’ll find. 

If you are creating something like a shampoo or bodywash, and want to step it up a notch, my favorite is PEG-7 Olivate (Olivem 300 from Lotioncrafter), used at 3%. It’s an emollient, lubricant, anti-irritant, solubilizer, and thickener — and it doesn’t suppress foaming/ lathering.

In addition, you can add a film-former like a hydrolyzed protein (used at around 2%) which will help the skin to retain moisture.

You mentioned using dimethicone which is also another good choice. If used, keep that at around 2%.

In my humble opinion, I would avoid petrolatum.