"懒洋洋的姿势" can be translated into English as "a languid posture" or "a lethargic pose".
"Languid" emphasizes a slow, relaxed, and perhaps somewhat listless manner, often with an air of elegance or indifference.
"Lethargic" conveys a lack of energy or enthusiasm, suggesting a more sluggish or inactive state.
Both expressions capture the essence of a relaxed and perhaps unenergetic stance, though "languid posture" might be slightly more poetic or descriptive in certain contexts. Choose based on the nuance you wish to convey.