A 54-year-old man with long-standing type 2 diabetes and obesity attends for routine review. His latest results show HbA1c 8.8% (73 mmol/mol), eGFR 80 mL/min/1.73 m² and urinary albumin-creatinine ratio 4.0 mg/mmol. He is currently on metformin 1 g twice daily and lifestyle measures. According to the RACGP diabetes handbook, what is the most appropriate next step in glycaemic management?