Never give a cat milk or soy milk b/c cats are lactose intolerant.
Lactose is a type of sugar in milk that is very difficult for cats to digest properly, often causing diarrhea or vomiting.
Cream is perfect for cats in small quantities because it does not have any lactose sugar in it at all.
Do not give your cat soy milk either. Soy milk is made from a grain and is not actually a milk product. It has sugar proteins in it that are not processed and cannot be digested by cats well.
If worse comes to worse, you could try giving your cat some plain yogurt. Yogurt has enzymes in it that actually aid in the cat's digestion, and some cat food manufacturers use yogurt in their dried food products. Also, when my cats get sick, I feed them unsweetened, plain yogurt to help them get their appetite back. And they love yogurt or cream and have never become sick from it.
Hope that helps.