Most of your simple sugars (honey included) won't provide much in the way of flavor (honey can provide a subtle flavor if used right, but won't provide sweetness, but the flavor in honey can be destroyed if you don't use it right, making it just expensive sugar). There's Belgian candi syrups (not the hard sugar but the syrup) that can provide a bunch of flavor, but I don't think they're a fit for a porter. Using any of the simple sugars is going to boost alcohol, and that's about as natural as can be. A lot of the artificial sweeteners aren't even fermentable. That said, boosters are going to have a flavor impact (malt like DME or LME will boost body and flavor in addition to alcohol, and simple sugars can actually dry out and lighten the body and flavor a bit, and in both cases can have an effect on the way the hops and bitterness are percieved). If you want something higher alcohol, best bet is to start with a recipe that's already designed to have the right balance at higher alcohol.
What are the ingredients in the porter kit? Let's start with that.