A 60-year-old man presents with a 6-month history of worsening pain and stiffness in both knees, especially after activity and at the end of the day. He notices some crepitus on movement. Examination reveals mild bony swelling and crepitus, with pain on passive flexion. There is no significant warmth or effusion. X-rays show joint space narrowing, osteophytes, and subchondral sclerosis. What is the most appropriate initial management according to NICE CG177?