A 49-year-old woman on stable levothyroxine therapy for primary hypothyroidism presents for follow-up. She takes 100 µg daily on an empty stomach. She has gained weight and reports fatigue. Her TSH is 8.5 mIU/L (reference 0.4-4.0) and free T4 is slightly low. She is otherwise well and medication adherence is good. According to Canadian practice, what is the most appropriate management?