I am in the same boat as you (shopping the clearance racks for my daughter due in October) I have tried to buy as much 12 month stuff as possible, as you can always put her in something a little too big, but never something that is too small. I have also bought some 9 month stuff as well. I hope it all fits!
I found a bunch of great deals on onesies and bought them no matter what size they are, as I have seen my nephews where them year round.