I have moderate to severe mitral valve for more than 7 years and no symptoms or progression...there isn't any specific treatment other than control blood pressure and my MVR has not progressed, Surgery is considered when ejection fraction drops below 60% and/or your left ventricle is larger than 40 mm at rest my be the guide, but if the size of the ventricle enlarges that may be too late to get a good outcome from intervention...thus the dilemma. Your condition may be related to the valve opening enlarged and the leaflets do not adequating close the valve during the pumping phase, and/or the leaflets are the under lying cause as a result of rigidity of the leaflets, etc.
A surgeon from the Mayo Clinic is on record of staing the biggest problem he sees is the patient has waited too long. If your symptoms are related to MVR, then valve repair or replacement may be the only option as consideration should be given intervention to provide a better qulaity of life going forward.
Hope this provides a perspective and helpful for you to better discuss your MVR with your doctor. It may be a good idea to consult with a surgeon so as to establish a good relationship with a surgeon you are satisfied has good surgical skill, etc.
Thanks for your questions, and if you have any followup questions or comments, you are invited to respond. Take care and I wish you well going forward.
Ken