Soft, padded, and comfortable like a cushion.
From 'cushion' plus the adjectival suffix '-y' (Old English forming adjectives from nouns). Emerged as informal descriptive language in the 18th century for upholstered furniture.
Cushiony is slang that became legitimate—it started as informal speech but became common enough that even upholstery professionals use it in product descriptions because it perfectly captures a feeling that formal words miss.
Complete word intelligence in one call. Free tier — 50 lookups/day.