Hi Lindsay. Like Mike E, I hope you do not mind this reply from a man! In my opinion these (http://www.wellie-boots.com/bullseye-full-knee-farming-boots.htm) are the only boots any self-respecting farmer would ever wear. Unless you really are a strange shape you would have no problems with calf size. If you are not at all fashion conscious, and are not worried about the price, these are the ones for you - and they will last 'forever.'
Enjoy your holidays,
Trevor M