This is possible but also requires a bit more coordination than just buying two seats. If no one checks in for the second seat, the airline may decide it's avai

This is possible but also requires a bit more coordination than just buying two seats. If no one checks in for the second seat, the airline may decide it's available if you haven't made special arrangements when booking. Air New Zealand (and I think some Chinese airline) also have a program where if you're traveling as a group of two, there are special rows in economy where you can buy out the middle seat for less than it would normally cost. These rows also have locking fold up extensions that fill the space between your seat and the seat in front, so if you and your partner are both pretty small and extremely friendly, you can both sleep lying down.