A 58-year-old man from Mumbai presents with progressive dyspnea, orthopnea, and lower limb edema for 6 months. Echocardiography shows restrictive cardiomyopathy with biopsy-proven cardiac amyloidosis (Congo red positive with apple-green birefringence). Serum and urine protein electrophoresis are normal. Cardiac MRI shows diffuse late gadolinium enhancement. What is the most appropriate next step in management?