I wore the perfect white dressy coat at my January wedding a few years ago. Sadly, it is no longer available, and the designer, Sofia Cashmere, isn't making anything like it this year. I looked for you, thinking it might be a great fit, if you could find a coat on sale.
While this is not what I had in mind for you, what about something like this?
http://www.saksoff5th.com/wool-blend-wrap-coat/0492824818099.html?start=114&cgid=Womens-Apparel-Outerwear#sz=132&start=1&location=18252&slotLoads=8
Note the coupon code for an additional 40 percent off.
And, while this is in black, it might be really stunning. And it wouldn't have to be cleaned as much:
http://www.saksoff5th.com/fur-collar-wool%2Fcashmere-coat/0497727886602.html?start=20&cgid=Womens-Apparel-Outerwear#start=1&sz=120&srule=Price+High+-+Low&location=3143&slotLoads=2
I realize this last suggestion is closer to $400 than $300, even with the coupon code. But it's an elegant coat in your size. And, for the money, much better than you could get at J Crew.