Hi Jack-
Welcome to this wonderful site. You will like the support and help you can get here. Everyone understands the situation.
If you have been told that surgery is needed, I would pay attention. Get a second opinion, if you want, even a third, but if there is agreement, then you need the surgery.
With my husband's aortic valve replacement 25 years ago, he knew he had heart problems because he had a murmur from rheumatic fever. But he ignored it and played competitive sports and did all kinds of very physical things. He finally passed out on the basketball court, and had his surgery soon after. However, he had been courting danger for many years.
With his mitral valve replacement, he was very, very ill prior, and also with the repair on the mitral, when he was even sicker. I don't recommend that you wait until you are very symptomatic. You won't like that at all. Things can go downhill very fast, and by the time he finally had surgery, he could barely walk to the bathroom without passing out and couldn't sleep at night except in a sitting position, and even then he couldn't breathe.
Facing this surgery is hard when you have symptoms, but you have lots of incentive, then, to feel better, when you're asymptomatic, it makes it seem unreal. Your heart is compensating for it's inability to pump efficiently by enlarging, and that is not a good thing.
Best wishes and take care.