Hi, a lot depends on how tall you are. E.g. I'm a size 16 (sort of, I'm sometimes a 14) but I'm 5'8", have a waist etc. and so don't look large. Right now there is an outfit on the r-hand side of the site that would be great for you -'Rotita', lime green and black. It may come up on your screen.
Go for a long, slim, slightly flared style with simple, geometric, strong colour contrasts which draw attention to the dress/outfit and not the wearer. Then go a bit mad with the hair, shoes and accessories. Hope this helps.