The more malt you use / higher original gravity, the sweeter the beer will turn out. Another trick is to use a low attenuating yeast such as Windsor or S-33, which will only attenuate to about 60% or 67%, respectively. If I were you, and willing to end up with the ABV up to 7-8%, I might aim for OG 1.088 (approximately), which with one of those yeasts should end up with around FG 1.030 and 7% ABV or more. A finishing gravity of 1.030 should be plenty sweet, with no lactose required.
Use any stout recipe that looks good to you, and just add extra base malt to bring you to about 1.088. If using extract, this is pretty straight forward. If brewing all grain, expect a low brewhouse efficiency around 55% for such a big OG. The more malt you use, the more you need. Might seem odd but it's true. So to end up with 5 gallons (for example), it wouldn't be unheard of to need 15-20 pounds of malt to achieve this. If you want to use less malt, it also helps to sparge a huge volume and plan to boil for 2-3 hours. This will improve efficiency at the expense of boil time. If this is all overly complicated, just add extract and be done with it. In any case, the goal of my idea is to end up with a nice high FG close to 1.030, that will be a creamy beer for sure.