For adventuring in Southeast Asia, I highly recommend bringing a backpack instead of pulling around a luggage.
A backpack makes more sense, especially if you will be going to beaches and moving from city to city.
They are more convenient to carry during times when you have to run after a bus or when you are booking it in the airport to get to your gate for your next flight.
I own an REI 40L Ruckpack (which unfortunately is no longer available). I will link it here once it is available again.
During most flights, I got away with bringing this size as a carryon and did not have to pay to check it in.
You also have to think about the weight of the backpack and how much you are willing to carry.
As a 5”4 woman, I was comfortable with carrying the 40L because any more than that was way too much and would get too heavy.
In addition, carrying a 40L backpack was not as “in your face” as the bigger sizes.
With the 50-70L, you really stand out like crazy because these sizes ARE GIANT.
If that’s your style and you can carry that much, then go for it.
Here are my recommendations for backpacks that are similar to the REI 40L Ruckpack: