A 22-year-old man presents with sudden onset pleuritic chest pain and dyspnoea. He is tall and thin, with no past lung disease. Examination shows trachea central, decreased breath sounds and hyper-resonance on the right. Chest X-ray confirms a 25% right primary spontaneous pneumothorax. He is haemodynamically stable and minimally breathless. According to current guidance, what is the most appropriate initial management?