A 56-year-old man with type 2 diabetes, obesity (BMI 32 kg/m²) and no known cardiovascular disease presents for review. Fasting plasma glucose is 8.5 mmol/L and HbA1c is 7.8% (62 mmol/mol) despite lifestyle changes alone for 3 months. According to Australian diabetes guidelines, what is the most appropriate next step in his glycaemic management?