While at the dealership, I sprung for the winter floor mat package:
Attachment 787
At around $104 for the set after taxes, they seemed a little pricy, but these are form-fitting exactly to the Micra. Further, they have considerable weight to them, and the bottoms have a texture that acts almost like velcro, sticking them in place on the carpet:
Attachment 788
Well worth the price tag, they look very capable of protecting my Micra's floorboards from the rigors of our winter. Plus, they have the "Micra" name molded in them (fronts only). :)