I would stay put because there if you move there is a small chance you will be bumped by a baby and the difference between the pairs is minimal.

I am tall, and would consequently move to 64A if I couldn't have one of the other really choice UD seats (64K, 62K, 62A) - I did precisely that at T-3d going to CPT in December when I booked at short notice - but you have 64K already.

You know that you will need to call BAEC if you want to choose 64A before OLCI opens even though it is now showing in MMB.