hi, thank you for providing the brief history of you. A thorough neuromuscular ENT assessment is guided. As mentioned by your doctor you have smaller passage of the left side of the nostril which is not allowing sufficient air to flow and surgery is of choice, then your doctor may be right as unitl the passage of the respiratory system is clean and opened the air entry to the body is restricted which leading to breathlessness as body don t get sufficient air. Also, for smell sense, it totally depends upon the Neurological system of your body. By taking training for it from a physical therapist who is a rehabilitation specialist , you can get help better. before undergoing the procedure of surgery you may need to take a pulmonary function test to assess the fitness of the lungs. As, if the PFT is normal than the breathlessness issue is not due to the nostril but due to muscle weakness. As you have already lived long years without any issues. Also, by strengthening such muscle groups of respiration your breathlessness issue can be solved. In case the PFT turns negative than you may need further assessment to decide for the surgery. Regards Jay Indravadan Patel