Coconut oil, but I only use it about once every six weeks. I don't want to weaken the hair strands. I also have curly and frizzy hair.
I put the coconut oil in dry hair, focusing mostly on the front/top and the ends, then leave it for anywhere from 15 minutes to two hours, then wash and condition as normal.
Also after I get out of the shower, about once a week or two weeks, I put in Moroccan oil before using my regular hair products.
https://www.moroccanoil.com/products/moroccanoil-treatment-original