Becky, this looks GREAT. Don't change a thing. Seriously. It's not even 'looks great for maternity', it's 'looks great, period.'
GP's the good doctor of maternity dressing, so listen to her! Do NOT be tempted or bullied or swayed into a change from your preferred style just now. There's enough change going down without that added hassle, except to take cognizance of and adjust to a new silhouette. But that doesn't mean a change in style *direction*, only slight adjustments of silhouette and points of emphasis.
You're supposed to look like pregnant yourself, not like pregnant other-blogger, right?
And yeah, KEEP the flats. If Angie can be fab in flats, you don't need to learn to hang your heels up high now, of all times in your life.
About the shirts, this one looks just perfect on you right now. So don't retire them yet! In fact, as Natalie says, you can always use them for layering even when they get to gaping --- tank under, or hey, if substantial enough, even over the partially unbuttoned shirt!
Oh, thanks for this thread, by the way --- I'm going to be a vampire and stick my teeth into some of these lovely links the other ladies have shared too! >:-[