A 65-year-old man with a 40-pack-year smoking history presents with chronic cough and exertional dyspnoea. Spirometry shows FEV1/FVC ratio 0.55 and FEV1 55% predicted with little reversibility, consistent with moderate COPD. He currently uses short-acting salbutamol as needed. According to Australian COPD management principles, which is the most appropriate next pharmacological step?