A 48-year-old man with established rheumatoid arthritis (disease duration 8 years) on methotrexate monotherapy presents with progressive joint swelling, morning stiffness of 90 minutes, and new subcutaneous nodules over his elbows. Recent labs: ESR 52 mm/hr, CRP 38 mg/L, RF 420 IU/mL, anti-CCP 145 U/mL. Hand radiographs show multiple erosions and joint space narrowing. He has tolerated methotrexate well with no hepatotoxicity. What is the most appropriate next step in management?