I do positioning flights for almost all of my international travel-it's just easier and less stress (for me). Of course, I'm also retired and time isn't an issue.
I've started looking more and more for positioning flights out of airports that have hotels IN the airport (like BOS, MCO, DFW) v. ATL, just for convenience. DD lives an hour from BOS so we use that a lot and I've found that AF/KLM flights are cheaper out of BOS than ATL, usually (at least on points). IAD seems to be a big hub for United (but it would probably be easier for you to fly to ORD?) and MIA or PHL for AA flights. (*I could be wrong but I don't believe IAD has an in airport hotel-PHL does-a Marriott, MIA definitely does not). DTW could also be an option for DL/AF/KLM and their in-airport hotel is nice, as well.
**I mention in airport hotels because I fly to the positioning airport the day before my international flight but if I were doing an all in one day trip
just in case something went wrong, it's nice to have a room/bed/shower within walking distance.
Which int'l positioning flight depends on where you're going and with whom you're flying. Also, if you check bags, obviously you need to account for baggage arrival time. BOS international terminal is E (usually) so if you fly Southwest, you'll have to get on a bus or walk from terminal B, where Southwest is said to use (I don't know, I'm all Delta/AF/KLM in BOS).
This is a pretty good article:
https://upgradedpoints.com/travel/airports/boston-logan-international-bos-airport/
Hope this helps!