A 32-year-old woman from rural India presents with progressive dyspnea on exertion and orthopnea for 6 months. On examination, she has an opening snap and a low-pitched diastolic murmur best heard at the apex with the patient in the left lateral decubitus position. Chest X-ray shows straightening of the left heart border and pulmonary congestion. Echocardiography confirms mitral stenosis with a mitral valve area of 1.2 cm² and normal left ventricular function. She is currently in sinus rhythm. What is the most appropriate next step in management?