Last year, I was facing a grueling 10-hour flight to London and knew my back wouldn't survive main cabin. I’ve found that the absolute best way to snag a Delta One seat without draining your savings is to keep a hawk-eye on the Fly Delta app right after check-in.
For my trip, I noticed a "Global Upgrade Certificate" option, but since I’m not Diamond Medallion, I just waited until 24 hours out. A discounted upgrade offer popped up for 40,000 miles. It was a total game-changer for my sleep! You can also call their desk to modify your existing reservation if you have spare MQDs.