We had a similar situation for an upcoming trip. It's 5 nights, but I could only get a discount at Poly for 4 of those nights. I ended up reserving AKL savannah for one night at the end of the trip. I then reconfigured our park plans a little so our resort switch day will be our AK day. I'm not looking forward to packing up and moving, but my DS12 is looking forward to seeing the animals at AKL and I've reduced travel time a little by making AK that day's park plans.
As PPs have said, I would book what is available now and just keep checking. Inventory changes constantly.