Hi K.,
My son (13 months old) can not tolerate cow's milk, but he can handle trace amounts of dairy, like cheese in a casserole.
Soymilk seems to upset our son, too, so we give him goat's milk and rice milk. (Rice milk is pretty void of any nutritional value, but we use it to dilute the goat's milk and make it last a little longer.)
Also, remember that you don't *need* to wean your son off of formula at exactly 12 months. This is not federal law. ;-)
You really have 2 ways of proceeding at this time. One is to keep him on soy formula for a few more months and then try cow's milk again and see what happens. The other way, if you want him off formula right now, would be to give him soymilk and/or goat's milk.
You can easily and inexpensively make soymilk at home; there are lots of recipes online.
Good luck!