The easiest way to do this BY FAR is to use alginate and gelatin. Gelatin is way easier to get than any of these two part silicone yokes. Also it does not shrink or discolour. It looks a lot like skin because of its translucency and even has a simular feel. A lot of the info on the net about moulding, casting and model making in general is dodgy so be careful.
If you are on a lo/no budget thing than plaster and latex is the way forward. Cheap and cheerful if not a little shrinky…