One thinker that comes to mind is Friedrich Schiller, who described gracefulness as the “beauty of form under freedom’s influence.”

When habits are being formed, they are conscious and deliberate. Gracefulness is the nature of practiced habits that are so deeply instilled that they seem effortless. 

For instance, when you are learning to have ideal posture, you need to regularly remind yourself to roll back your shoulders, and undo your slouch, and speak at a reasonable pace. After this becomes habit, you don't think about it, you just do.

Schiller applied this concept to Kantian ethics. If you don't buy into Kantian ethics, the idea essentially works with other ethical models. Gracefulness is when ethics leaves the classroom of calculations and thought experiments, when a person's disposition is transformed to conform to goodness. Goodness becomes intrinsic to the person's character, following effortlessly from their disposition and inclinations. In Schiller's words, "the ethical sense has at last so taken control of all a person’s feelings that it can leave affect to guide the will without hesitation and is never in danger of standing in contradiction of its decisions."

Gracefulness is fine when times are easy, but hard times give way to dignity. Dignity is remaining composure through pain and adversity -- “a power independent of suffering."

Schiller describes a man whose “veins swell, his muscles become cramped and taut, his voice cracks, his chest is thrust out, and his lower body pressed in,” but regardless of the physical trials, “his intentional movements are gentle, the facial features relaxed, and the eyes and brow serene.”

These ideas of gracefulness and dignity are both based on "leveling up" from one's natural state. Gracefulness comes from learned skills that become natural and effortless, and dignity is a trained determination to remain resilient through suffering.

Source: https://plato.stanford.edu/entries/schiller/#GracDign