A 52-year-old woman presents with a 3-month history of progressive swelling and pain in her left leg. On examination, she has pitting edema, dilated superficial veins, and skin pigmentation changes over the medial aspect of the ankle. Duplex ultrasound shows incompetence of the greater saphenous vein (GSV) with reflux lasting >0.5 seconds. She denies any history of DVT or leg trauma. What is the most appropriate initial management for this patient?