A 68-year-old ex-smoker with chronic cough and exertional dyspnoea has spirometry showing FEV₁/FVC ratio 0.55 and FEV₁ 45% predicted, consistent with COPD. He uses a short-acting bronchodilator as needed but remains symptomatic with two exacerbations in the last year. According to NICE COPD guidance, what is the next most appropriate inhaled therapy?