A 72-year-old woman with a history of type 2 diabetes mellitus and hypertension presents with a 3-day history of productive cough, green sputum, and fever (38.5°C). Her respiratory rate is 24/min, heart rate 110/min, and BP 130/80 mmHg. Auscultation reveals crackles in the right lower lobe. Her CURB-65 score is 1. What is the most appropriate antibiotic choice according to NICE guidelines?