We went with rice milk. It tastes kind of like skim milk, but a little sweeter. Beyond drinking milk, make sure you check the ingredients of your food. Often milk is listed in the allergy section, but sometimes it isn't. You need to avoid anything that lists milk or casein. Milk protein (casein) is hidden in a lot of foods - some brands of bread, crackers, cereal, etc.
It can be hard to get dairy out of your diet at first. Your first trip to the grocery store may be long because you will need to read the ingredient lists on everything you buy. But after your first few trips, you'll have a list of brands of food that are ok, and you'll know which to avoid, and it gets easier.
As for hydration, have you tried any of the water enhancers? They are little things and you squeeze a small amount into water to give it a little taste. It's a little bit of flavor without all the sugar of kool aid or lemonade.
Good luck, I hope it helps.