Credit cards which earn frequent flyer points is a popular way to earn frequent flyer points. You can receive thousands of points on everyday spend. And, many of these cards offer generous signup bonuses! Compare to find the credit card that best suits your needs.
Keep in mind that onboard upgrades don't change the amount of FF points/SC's earnt on a flight from the original booked class. Not applicable in your case for this journey, but something to keep in mind for the future.