Both are right, but comfy is more informal. The soft mattress makes it comfy the warm blankets make it cozy|@sushimasters the. Comfy的同義字@sushimasters the best way to understand this is to imagine a very comfortable bed.
Comfortable is the state of comfort. This bed was designed to provide comfort to its. It's just used to place emphasis on.
More than 100 answers from native speakers about natural usage and nuances of comfy. Comfortable 的同義字@slato they both mean comfortable, but comfy is a cute informal way to say it this bed is comfortable.