Not sure this is posted to the right forum, but I think being 50 years old provides its own answer.
No, I don’t think it’s selfishness to decide that 50 is a prudent age to avoid pregnancy. There are risks involved. Moreover, at that age, even though your economic situation is secure, you have to think ahead. Your child will be hitting college when you’re nearly 70. If retired, would you be able to provide a college education for him or her? Will you still have good health at age 65? Will you still have the patience at age 65 to deal with teen angst? You may be in good health now, but as my wife and I are discovering, over age 50 even good health is not a guarantee that you’ll remain that way through your 50s.
There’s nothing wrong with being prudent and not over-extending yourself.
You’ve done your duty, enjoy your good health with your husband. Prayers that you’ll continue to have a healthy life for many more years to come.