You will love the fact there are very few cars and fantastic roads in that area, I've spent weeks up there, crossing in and out of the Borders.
You could book in advance, or drop into the ever-so-friendly Tourist information in Seahouses, they can phone ahead to an available B&B. Cheapest way of a week's holiday we found, was getting a cottage between 4 of us. Makes it dead easy getting stuff dry. Keep quiet if you have a great time, don't want hoardes of tourists finding out about it :t