Have you consulted with a very experienced Thoracic/cardiovascular surgeon? If you have not that should be your priority. You are right at 5.4cm (mine was repaired at 5.2 cm) you are in the criical range of needing surgery, but that depends on a lot of factors. Get a professional opinion, besides a very, very experienced surgeon in a major medical center, I would find a cardiologist wo is an expert in aortic diseases, they would do all the appropriate exams, imaging, etc and give you the path forward. But don't wait, you are truly in the critical zone.

Keep taking care of yourself, stay active, if you are in good shape as you say, surgery and recovery will be way easier. I was in great shape when I had mine, the surgeon gave me >99% probability of not having complications. Surgery is tough, but I recovered quickly, was out of the hospital in 5 days and back to work in 3 weeks.

All the best to you