A 68-year-old man with known heart failure (LVEF 35%) presents with increasing ankle swelling and breathlessness on minimal exertion. He is currently taking ramipril 10mg od, bisoprolol 5mg od, and furosemide 40mg od. His BP is 110/70 mmHg, HR 78 bpm, K+ 4.2 mmol/L, eGFR 55 ml/min/1.73m². What is the most appropriate next step in his pharmacological management according to NICE NG106?