I find you get ample sweetness with a little blend of caramel and munich malts - go lighter or darker based on your own goals and preferences, and Vienna works too. Frankly, if you're finding enough sweetness in the IPA's you buy but not your own, then this should be enough as most recipes stick to this route. Remember that the base of a great IPA is all about the balance between bitter hops and sweet malt, and most brewers can do it with just these basics.
If you want to take it a step further than most American IPAs, try Maris Otter for your base malt instead of US or German pale ale malts. However, if you find your beers to be too dry, do not go across the pond for your yeast - be sure to stick with the US ale yeasts, not English or Irish ones. You can also mash at higher temps for a fuller body which adds to the perception of sweetness, if not actual sweetness, and do not add any sugar to your boil, which (possibly counterintuitively) lightens the body and thus reduces the perception of creamy sweetness in favor of crisp dryness.
If none of that works, add an unfermentable sweetener like lactose. I haven't tried a "milk IPA" yet but who knows?! Cheers!