You're brave for flying Jetstar. A couple of years ago we booked what we thought was a flight from YBBN to NZQN with Emirates in J class. Ended up in a QF 737 and in a Y seat with JQ. The NZAA-YBBN leg was on an Emirates A380 thankfully. When you have a fused back, Jetstar seats are worse than sitting on a park bench.