I’ve only done medium-haul with my 2 year old before (oman, but with a stop en-route in istanbul to split the journey) – in a weeks time we’re headed to the Seychelles so reading this with interest.
The inflatable footstool/bed thing works well, we’ve also used this before https://www.keepemquiet.com
new toys are pretty good generally. Find out if (wherever you stop) there’s a lounge with a kids area, and get access to it. Some of the lounges have things like ball pits and so on in a noise-blocked space – so you can let the kid burn off a couple of hours more energy before going back to sleep.
I’d actually consider 2 or 3 stops en-route with maybe a day or 2 in between if you can find a route/schedule to fit, it would make things a lot more pleasant.
One final point. A lot of planes have ‘plane police’ on them. If you’re not good, they will come and get you..