Hi Dawn and Jeni
I won't be joining you on the November 2025 NZ trip because I am going in three weeks time (counting the days!). I went on the same trip in 2024 and loved it so much that I am going again 🙂 If you have a look at the 'reviews' section of the Community board, you will find a few of my hints and tips.
Regarding the flight upgrade, I would definitely recommend it if it is within your budget because, although three of the four legs are night flights, you are basically travelling for almost two days each way, so comfort is important. I treated myself to business class and feel it was worth every penny. The Singapore Air cabin crew are amazing and seem to anticipate your every need long before you realise you need it! Another tip is to register for the Singapore Airlines 'Krisflyer' programme. A long haul trip like this will earn you quite a few Krisflyer miles which can be used in the airline shop or put towards flights with other Star Alliance member airlines.
You are right that it will be summer when you travel but NZ weather turns on a sixpence so I would recommend having a lightweight waterproof jacket that you can pop on and off as you need it (this will also come in handy if you do either of the optional jet boat excursions.) The coaches that JY use are very spacious and comfortable but I agree that you may find long cotton trousers rather than shorts are preferable on travel days. I like cargo trousers because the extra pockets are handy for your camera/phone - trust me you will want to use one of those frequently on this trip!
Happy to help if you have any other questions
Start counting down - you will have an amazing time
All the best
Mandy