i think if you are considering SOing a damier galliera, you might as well go for your HG. The mahina L is a beautiful bag... but of your three choices i vote for the trevi pm.
I originally voted for the Trevi but after reading what you currently have, I am changing my vote to the Galliera. You don't have a mommy bag yet. The Galliera is a great, fashionable mommy bag.