I recommend the Pengsoo heated hair roller.

The price is a bit high at around 25,000 won, but since it uses USB to generate heat, it lasts a long time, which is good.
Before I bought the heated hair roller, I often had a hard time because my bangs would stick to my forehead when the rain was on and off like it is now.
But after buying this product, my worries about my bangs have definitely decreased a lot >_<
When I go out, I wear warm hair rollers, and then I take them off when I go indoors. That way, I can maintain tight, bouncy bangs no matter how humid the weather is. It's the best!
If you find it difficult to wear it outside because you are self-conscious about other people's stares, simply curling it indoors for about 10 minutes will bring your flat bangs back to life.
If you're struggling with your bangs, I think it's worth considering buying :-) bb