I would indeed wear what I would wear to a similar wedding in New England in August – just without any white accessories. “Resort,” to me, means that tropical looks and open-toe shoes are standard. I wouldn’t wear closed-toe pumps or dark colors in Puerto Rico or on a warm-weather cruise either.
Gourmetmom made another good point - if your body shape differs significantly from what clothing makers use as their standard, find a good seamstress who can alter clothes for you.
I have used a dressmaker/tailor on occasion and found it to be money well spent. Once, it was to alter a skirt that I had owned for decades but still was in excellent shape – she dropped the waist and made the waistband longer as well as shortening the length of the skirt that hit mid-shin to just below the knees. With these inexpensive alterations, I’ve been able to use the suit for several years longer.
She also made a dress more fitted at the waist than it would have been otherwise (the dress was a size or two larger than my usual).