I recommend Mise-en-scène Curling Essence.

It is humid and I sweat a lot in the summer, so my hair loses its shape quickly even after using a curling iron or getting a perm. That is why I purchased this curling essence. If you squeeze out a coin-sized amount and apply it to wet hair after washing it, the curls really last a long time. It is so convenient to keep the curls intact even in humid and sweaty conditions. The price is on the affordable side, the performance is great, and since it comes in a really large size, I can use it for a long time.