"Downiest" is an uncommon word derived from the adjective "downy", which refers to something soft and fluffy like the feathers of a bird or the delicate texture of a flower. While there are limited synonyms for "downiest", we can explore alternatives that capture the essence of softness and texture. Similar terms could include "fluffiest", emphasizing the quality of being light and airy, or "feathery", alluding to the downy nature of feathers. "Softest" and "plushiest" are also viable alternatives, emphasizing a soothing and comforting texture. Although "downiest" may be a unique descriptor, these synonyms effectively convey the desired characteristics of softness and fluffiness.