My apologies if this has been asked and answered; I haven't been able to find a good answer in a search. I'm currently Silver on NW, and will be again next year; I tend to fly between 25,000-45,000 miles for leisure travel most years. In a month or so, however, I'm going to be starting a job that will take me out of town about 50% of the time, so I'm trying to figure out what my best option for accrual will be starting in January. I don't have a great sense yet of how much mileage I'll end up earning or how much I'll be able to consolidate on one carrier.

The perk I appreciate most about NW is, of course, the great availability of F upgrades on domestic travel even for low-tier elites. United E+ would probably be "good enough" for my purposes, as it's leg room I really care about; I'd rather not do much more flying in regular Y than I do now.

The catch is that I don't fly so many miles that I particularly want to redeem for free trips to Europe or Asia; I'd much rather buy and upgrade. I really only manage to get across the pond once a year on leisure, but with NW upgrades are both costly (requiring B fares) and hard to get. Is there another program I should be considering that would allow me to use my miles to upgrade internationally once a year, without giving up too much in terms of domestic upgrades? I'm based in BOS, if it's relevant.

Thanks!