Welcome to Flyertalk. Personally, I NEVER use double miles to book anything. I find that I can either book far in advance or with very little notice. It's the mid-range planning that tends to be troublesome.

Here's a handy tool many of us use to find open award seats:

http://usr.v7.com/wpaa/

Give it a try. Booking award seats is an art in itself, but you'll get the hang of it.