I like M names too, especially for girls.
I like your idea of Miller and Marnie.
Some more M I like:
Melusine, Mirande, Mabel, Myrtille, Melisand, Meredith, Marina, Marielle, Marisol, Marianna, Merryn, Meriel, Mazarine, Melisse, Marjane, Margot, Magdalene, Manon, Marguerite, Marion, Majolaine, Mirabel...
Mortimer, Melchior, Matthias, Mathurin,Magnus, Marcel, Maurice, Maxence, Myron, Merlin, Monty/Montgomery, Morton...