편안히 is conjugation form from 편안하다 편히 is conjugation form from 편하다 편하다 and 편안하다 both mean "comfortable" But, 편하다 has nuance of "easy, convenient" 편안하다 has nuance of "peaceful, calm, cosy" 편안히 means "comfortably and peacefully" 편히 means "comfortably and conveniently"