Hello Swede, pull up a chair and make yourself at home. Gosh, December is going to be a busy month 
flowers - aaah, it's great when you have a legitimate reason to wander around the babywear sections. There is something about white baby-gros that never fails to make me broody (oh, and teeny, weeny baby socks).
LoveYouForever - glad you are feeling happier. It's a shame DH isn't for budging but December is getting ever closer, and your reasons for waiting are sound.
amiready - As far as I know the school year cut-off date around here (Surrey) is the 1st September (but don't quote me on it). I can see your dilemma and I have to confess I would prefer an Autumn term baby too. DD is old in her year and would have found starting school at just 4 very hard.
I think it all boils down to just how important it is to you (and your DP) that you don't have a child that's very young in their school year. If you aren't going to feel fully excited and enthusiastic about ttc in December then maybe Jan would be better?
On the other hand, if you were very lucky and conceived straight away in Dec, there is also every chance your baby would be on time or late. However much you try to plan things, you are very much at the hands of fate when it comes to ttc. I think that is what can make it such a scary business (especially if you are someone that is used to planning and being in control)