A 51-year-old woman whose last menstrual period was 14 months ago has frequent, disruptive hot flashes and night sweats causing insomnia. She has an intact uterus, no personal or family history of breast cancer, venous thromboembolism, or cardiovascular disease, and a normal blood pressure. Lifestyle measures have not helped. She wants the most effective therapy for her symptoms. Which of the following is the most appropriate pharmacologic regimen?