Sorry I haven't bought one but will keep an eye on responses, as I need a dress too! That's not much help to you, is it??
Will you have enough of a bump at 14 weeks to warrant a maternity dress? I definitely don't mean that to sound rude btw, just they are expensive!! Maybe you could swap the dress you already have for one in a slightly bigger size?
I am preg with DC3 and although I had obvious bumps at ~14 weeks, I could still get away with wearing normal clothes, if they were forgiving in cut - i.e. empire line/floaty, etc.
I always find the maternity stuff drowns you in the early stages, as they are cut for when you are much bigger, even the one's that are clingy. If it's any help, I always have to go down a size in maternity dresses - they seems to size up everything rather than just the bump, so the bust, etc is always hanging off me. I am a sz12, D-cup boobs, so not skinny and I always need a 10 in maternity dresses. I wish they would just make the bump part bigger, but then I only tend to put weight on around the bump (so far anyway!).
However, I have a wedding to go to at 37 weeks and I will be mahoosive in the bump dept!! Already about 25 weeks and people are shocked at the size of the bump!
Keep us posted and Congrats and Good Luck!!