Prices are quite high from Dec 7 to Jan 7, as there is very high demand. You pay 50%+ more for those dates, and this has been the case for every year in the past few decades. Air NZ does have an interesting option on a few of their planes: Sky Couch (or something like that name). Only offered if 2 people are traveling, you pay for 3 Y seats and get a row of 3 seats that fold into a bed; fine for 2 people snuggling ... quite a clever idea, and better than PE, at least for sleeping. Food etc. is Y though, as is the normal non-couch legroom.

You really have no alternatives if locked in to those dates, except maybe flying via China or Malaysia with a stopover. Air Asia X does offer an LCC business class, which may be an alternative for you.