A 30-year-old man with a history of intermittent wheeze presents for routine review of asthma. He uses a salbutamol metered-dose inhaler as needed about 3-4 times per week and has required an oral corticosteroid burst once in the last year. Spirometry confirms reversible airflow obstruction. According to the Canadian Thoracic Society 2021 asthma guideline update, what is the most appropriate change to his controller therapy?