A 5-month-old boy is brought to a metropolitan emergency department with 2 days of coryza, cough and increasing work of breathing. He was born at term and has no chronic illness. On examination he has tachypnoea, subcostal recession, widespread crackles and wheeze, oxygen saturation 93% on room air and is feeding slightly less but still taking most feeds. There is no focal consolidation on examination. Which of the following is the most appropriate management?