If you don't fancy the price of premium economy or business class, you can get some great deals at the literal last minute. Go through with your flight as norm

If you don't fancy the price of premium economy or business class, you can get some great deals at the literal last minute. Go through with your flight as normal, check in, go through security, and find a member of staff for your flight. Ask how much an upgrade costs, and if they have the space available, they're open to offers. For example, about 5 years ago I got economy+ on British Airways LHR -> LAX for $200, and business offered for $600 or $700 IIRC. Not bad for a 12 hour flight!