A solid cream soap lasts noticeably longer if it is allowed to dry out between uses. The main thing that wears a bar down is sitting in water or on a wet surface, which softens the outer layer so more soap dissolves or sticks to the dish instead of your skin.
Keep the bar on a soap dish with drainage holes or ridges so water runs off and air can reach the underside. Avoid leaving it in a puddle on the sink edge, on a wet shower shelf, or in the bath water. In a humid bathroom, choose a spot with some airflow so the bar dries faster. When the bar gets thin, you can press the remaining piece onto a new bar while both are slightly soft, or keep it by the sink as a hand-washing bar until it is gone.
Storage also affects the fragrance and feel. Keep the soap out of prolonged direct sunlight and away from strong heat sources, which can dry it out or dull the scent over time. How long a 125 g bar lasts depends mainly on how often it is used and how much water it is exposed to; keeping it dry between uses is the most effective way to make it last longer.