A 62-year-old woman presents with a 3-year history of progressive pain and stiffness in both knees, worse in the morning and after activity. Physical examination reveals bony enlargement of the knees, crepitus on movement, and mild varus deformity. Plain radiographs show joint space narrowing, osteophytes, and subchondral sclerosis bilaterally. She has tried paracetamol 500 mg thrice daily for 2 weeks with minimal relief. What is the most appropriate next step in management?