편하다: to be convenient, to BE comfortable 편안하다: to FEEL comfortable, safe, relaxed, with ease of mind. Also worth noting is "편리하다" which also means "to be convenient" where "리(利)" means "benefit" or "gain". It's an expression for something very specific such as functionalities, rule, system, etc

편안(便安)하다 = to be safe and secure 편하다 = to be comfortable (leisurely) While they share a character in common (便), its primary meaning is "direction" and it is not helpful here to distinguish the 2 words. But the character, 安 means safe because the pictograph shows a woman under/inside a house. It's used in other words like, 안전 (安全, safety).

편하다: to be easy/casual/plain 편안하다: to feel comfortable/relaxed