Budget Travel - BKK-SYD/AUK-SCL + upgrade

I may be taking a 3 month trip from Bangkok to Santiago, July to October. What seems the least stressful approach (I'm 68) is via Sydney or Auckland .. and thinking of booking separate return tickets for each leg so I can rest a day.

The options from BKK to Sydney include Emirates, BA, & Qantas.

LAN & Areolienas seem the best options for leg 2

What I'm wondering is the best strategy / probability of getting / buying upgrades and what those upgrades would probably cost.

Any constructive advice appreciated.

Hi old_expat, welcome to FT!

The first thing to say is that it is always best to expect to travel in the class for which you are ticketed. If an airline needs to upgrade pax from Y to J then those pax with the highest FF status on that airline will generally get priority. if you have low/no status with the airline concerned then there is next to no chance of you being upgraded. Do you have status with any airline?

I had a very brief look on expedia and BKK-SYD-BKK in Y leaving in July returning in Oct should cost roughly US$1000. In J the price is more like US$3000. BKK-AKL-BKK for the same dates is more like US$1500 in Y and US$3500 in J.

SYD-SCL-SYD on AR in Y is about US$1000 in Y and US$3000 in J.

One option might be Air Asia from KUL-MEL/OOL in their XL class (a J seat with no-frills service) and then a 1 hour hop to SYD.