A 55-year-old woman presents to her GP with a 3-month history of fatigue, pallor, and shortness of breath on exertion. She has a history of menorrhagia. On examination, she appears pale and has conjunctival pallor. Blood tests reveal a hemoglobin level of 8 g/dL, mean corpuscular volume (MCV) of 70 fL, and low serum ferritin. What is the most appropriate next step in management?