I am so invested in this thread. OP, you'll have ot tell us how it goes.
Ignore the people saying no to white. Yes, it looks better on thinner people. But doesn't everything? They will look fine on you if you wear them with confidence. Half the key to white is just how cool and crisp it looks - that's the punch that elevates the outfit.
I do second the person saying buy what FITS. Do not do what I do which is buy things a hair too tight since i am "losing weight." For this weekend, but fir the size you are, no matter the size.
I would high tail it down to SPringfield, to the Talbot's Clearance store there. SOOOOOO Cheap, and the last time I was there it was all summer stuff- last year's, but a huge slection and you can pick and choose.
Also, was just looking at Ann Taylor - they have 40% off sale dresses (maybe today only) - check out these, depending on your body shape they may or may not work 9they only go to size 14, but sometimes AT is cut generously):
this with a seater or jacket to cover arms:
http://www.anntaylor.com/ann/product/AT-Weddings-Events/AT-Honeymoon/Colorblocked-Maxi-Dress/300847?colorExplode=false&skuId=13439910&catid=cata000047&productPageType=saleProducts&defaultColor=1422
this might work for me, but I am not super well endowed, so might not work for a larger chest:
http://www.anntaylor.com/ann/product/AT-Weddings-Events/AT-Honeymoon/Painted-Herringbone-Maxi-Dress/300849?colorExplode=false&skuId=13376406&catid=cata000047&productPageType=saleProducts&defaultColor=2666