I'm getting ready to purchase a flight on DL (through ATL and AMS) to CPH 14-24 August and have a few questions for those with more tatl experience on DL. My main priority is sleeping on the flight.

I've been able to sleep in economy class in US Airwarys tatl before, so am not sure paying for comfort plus is worth it. I'm 5'4", so leg room isn't a huge issue.

Have read that DL offers passengers the opportunity to pay for upgrades at check-in. Is there any chance they offer paid upgrades to someone in economy on a V fare? Is my chance increased if I am already in comfort plus? (I know BA will sometimes allow paid upgrades, but only if the person is booked into PE.)

Finally, is F a good product on DL? I might have the chance to upgrade with a work certificate if I buy a full-fare Y/M/B ticket in economy. But that's several hundred dollars more.

Thanks for any information you can provide!