Did wheeled suitcase and small rucksack last time when there was two of us. Broke twice on dodgy roads in SEAsia. This time round I’m doing big rucksack as it’s not going to break walking off a pavement and it’s nice to have hands free carrying. Smaller backpack on the front for tech which comes in the cabin and is also a daybag if needs be.
I’d go with backpack every time, the roads/pavements are not always flat and so you’ll be damaging your luggage with every knock, even if you get a good one. Plus there’s a lot of stepping on and off curbs if you’re moving around and that’s more hassle than a decent backpack.
Bali probably has the most of the kind of people you describe, then Phuket, then Bangkok, but Phuket and Bangkok you can avoid it easier as there’s more long termers there. Bug spray and stuff you can get on arrival. Got to go walking in the heat to get acclimated and eventually the sweating will drop off but it can take a while. If you can use a fan Vs AC and you’ll get used to it quicker.