A 35-year-old man with persistent asthma (on inhaled beclomethasone 250 μg twice daily) presents with 4 weeks of progressive dyspnea on exertion, nocturnal cough 3 times per week, and morning wheeze despite adherence to his inhaler. Peak expiratory flow (PEF) is 75% of predicted. Spirometry shows FEV₁ 68% of predicted with incomplete reversibility after salbutamol. He denies recent infections, new triggers, or medication changes. What is the most appropriate next step in asthma management?