A 53-year-old woman presents to her primary care provider's office reporting a persistent low mood and a significant loss of interest in her usual activities, including running and playing the piano, for the past two months following a family bereavement. She describes difficulty initiating and maintaining sleep, a notable decrease in appetite leading to some weight loss, and pervasive feelings of guilt and worthlessness. Her medical history is significant for diet-controlled hypertension, with her last recorded blood pressure reading being 132/84 mmHg at home. On physical examination, her vital signs are BP 130/80 mmHg, HR 72 bpm, RR 16/min, Temp 37.0°C. She is alert and oriented, but her affect is subdued. She is seeking medication to help with her symptoms but expresses a strong preference for an option that will not adversely affect her blood pressure control. Which of the following is the most appropriate initial antidepressant choice for this patient, and what is the crucial vital sign to monitor during the initial phase of treatment?