Flannel is probably one of the least luxurious, yet most comfortable fabrics out there, so how could you say no to a flannel dress? The key to not looking like you just got out of bed is to accessorize, as with most anything else. A leather jacket, bold necklace, and heeled boots tie in the look so you're still comfortable, and casual, but not a slob- at least, if you are in fact a slob, no one will think you are ;)
Jacket: Gap. Dress: Banana Republic. Tights: Forever 21. Boots: Rachel Comey. Sunglasses: Ray Ban. Necklace: Banana Republic. Bag: Anthropologie.