My one and only recommendation is Celestial Crowns! The customer service is sensational, and the owner is extremely kind. I was her first buyer from the state of Alaska, so she spontaneously gave me a free gift with my order. The shower caps come in numerous sizes, which are perfect for covering locks, box braids, twists, and even large volumes of natural hair in the shower.
I personally don’t prefer to wear a shower cap, because I find the moisture from the steam keeps my locks hydrated. But if you find one necessary for yourself—whether it be because you like to submerge your head under the shower, for deep conditioning treatments, or for bleaching/coloring processes—that’s definitely the brand I recommend.