I too have a lactose intolerant toddler....the best milk that i have tried is dairy ease by land o'lakes. i never had a problem w/ her throwing her milk up unless she was sick or her allergies were acting up and she had a lot of gunk in the back of her throat. it just coated her throat and made her vomit. her problem was either constipation or diarrhea depending on how much milk she had. i put her on lactose free milk when she was an infant and have stayed on lactose free milk cause i am lactose inolerant too. some of the other lactose free milks are pretty thick. you might also want to try the organic lactose free milk out there, i forget who makes it but it has a picture of a house on the front. i think kroger sells it and so does whole foods or wild oats. if you are military, the commissary sells it too. dairy ease has been the easiest, and of course every once in a while the real deal sneaks up on her in cheeses, ice cream, or at daycare, but she seems to do better the older she gets. land o'lakes also makes lots of other lactose free foods.
oh, and you could try rice milk...we did that for a while when we had some problems going from formula to regular lactose free milk. it was easier on her stomach. i would cut back on the amount you give her too, the doctor told me to make sure she got at least 4 servings but to supplement w/ other things too.
hope this is helpful.
M.