Congrats on getting rid of your non-mortgage debt! Permit me to put on my Captain Obvious cap and encourage you to avoid new debt on credit cards as you pursue this.

If you choose the obvious goal of Singapore Airlines, you will need KrisFlyer miles. These are easy to earn, nearly all the major flexible points cards can transfer to them. The bad news is that I understand Singapore doesn’t release a lot of the luxury seats for award travel. That was before the pandemic, I assume things won’t change, but don’t have actual knowledge.

If you choose to go with Singapore as your target airline, most any of the good flexible point cards will do. Because the annual fee is low, and the earning rates are good, I personally am a fan of the Citi Premier combined with the Citi Double Cash, but there are many options. You could collect bonuses from other flexible point cards as well of course. You mention debt and turmoil, if that shows up in your credit rating you’ll want to get whatever you decide will be your key card(s) first and verify that your credit rating is good enough before applying. Unless you are using your airline cards extensively for boarding and luggage privileges, they may not be much help. Before canceling all of them, think about how shrinking your amount of total credit can hurt your credit rating if it causes your utilization percentage to go up.

if you want to shoot for one of the other airlines still flying the 380, you may have a slightly different path, but whichever you choose, you run the risk of the airline joining the crowd and grounding the big airliners. Flexible point cards would definitely lower the risk. It may be worth researching which flexible point systems are most oriented towards the airlines still flying the big metal.