The reason why I chose a 0 degree bag is because 1) I'm a cold sleeper and 2) Most temps will be 18 degrees and above. As far as I'm concerned all bags are rated too low!
No my dog is too big and squirmy to sleep IN the bag but she can be rambunctious (especially in the mornings) and jump on me to wake me up so the bag should be able to hold up to her jumping on it (and me ).

I did come across a -20 bag by Ledge called the River that's on sale. It is 7 pounds but considering that my entire cooking and serving set weighs less then a pound, I could handle 7 pounds if it's warm enough!