A 3-month-old boy presents with 2 days of coryzal symptoms and increasing work of breathing. He has tachypnoea, subcostal recession and widespread crackles and wheeze on auscultation. Oxygen saturation is 93% in room air; he is feeding slightly less but has adequate urine output. A nasopharyngeal swab is positive for RSV. According to paediatric guidelines, what is the mainstay of his management?