I'm not sure what you mean by "almost plus-size" (in my experience, a lot of women who put themselves in that category are not very big at all!). But regardless, size definitely shouldn't stop you from wearing whatever costume you like. What kind of ideas are you thinking of? That might help us make some more helpful suggestions.
If you plan to ride rides, I would keep move-ability in mind. It would not be easy to get into a ride at
Disneyland wearing Belle or Tiana's ballgown, for instance! But Belle's village dress would be pretty easy to move in, and Belle's pink or maybe green dress from the movie would probably be OK. Many of the princesses offer multiple dresses with different ranges of comfort (and difficulty in constructing). Sleeping Beauty has her Briar Rose outfit; Snow White has her "peasant" dress; Ariel has her "Kiss the Girl" dress, her wedding dress, her pink dress, the blue dress at Disneyland, her mermaid form...
Last I heard they will NOT be letting costumed people in the parks before the party, so if you're visiting the parks earlier in the day, you also may need a costume that is easy to get on, will fit in a locker, and doesn't require extensive make-up. Since Disney may waffle on that position for some time, I would plan for a costume that fits those qualifications regardless.
And of course per the rules (at least last I saw), if you wear a mask, your eyes must be CLEARLY visible. Don't go in with a very nice mask that has two tiny eye-holes and then get mad that you get kicked out (as someone on another board did last year). Mostly I don't think I'd cover my face, period.
If you want obscure ideas, you could be from Pirates of the Caribbean--I think there are only a few women in there, but most are probably if anything larger than you. Your thinner friend might want to be the redhead, and she'd probably get a lot more attention than you, since she'd be more recognizable....depending on your preferences, that can be a good thing or a bad thing. (Some people might get a touch jealous--I would!--while others prefer not to get attention and would rather people be looking at their friend instead.)
I don't think we're going to, but I thought it would be fun for my friend and I to be Anne Bonny and Mary Reid from the walls on Pirates of the Caribbean. Recognizability might be low (again, I don't know if you consider that a good thing or a bad thing!) and that 1960s hair might be annoying to do
plus I don't think you'd be able to bring in the weapons. The costumes, aside from the boots, would be pretty easy to put together, though, and move-ability is high. Heck, Anne even gets a purse!
I can't think of many prominent Disney women who aren't villains (did you want to be a villain?) and who are "large", and I think the ones that do exist would again be bigger than you. But someday when I'm older and/or bigger, I'm definitely going to be one of the fairies from Sleeping Beauty.
