Yeah, zig zag is what I meant. I didn’t see the photo with the fallen over tree, but that’s always something that can happen when you plant trees because their roots need time to grow in. You can put two poles in the ground and use some rope to tie the tree to the poles so it can’t fall over. You have to make sure periodically that the rope isn’t cutting into the tree, though and after one to two years you can remove the poles. I’ve never planted them myself, but friends of mine have some. I’d rather go for the pencil trees than bamboo because bamboo isn’t really non-see-through unless you plant a little forest and it also grows like hell, so you’ll need to manage it constantly.
If privacy is your top priority I’d go for gabions. It’s those stone/pebble filled metal mesh cages used to build garden walls. They’re definitely not see-through and you can plant them with evergreen plants that will cover the entire wall over time. That’s probably your best, but also most expensive option and I’m not sure whether they’re available in Thailand, but any metal shop could make them for you. They would need to be Zink coated afterwords or Zink powder coated and then powered coated with a regular paint to prevent them from rusting away.
Alternatively you could just put a couple of stainless steel poles in the ground and connect them with stainless steel wires and then plant that heavily with evergreen climbing plants.