Hi......and welcome to FT. I donīt think there are any direct flights from BOS-MEX. All of the connecting flights use 737s, 319s and 320s, so there is nothing special there for F. CO and UA look like they codeshare as do Delta and Aeromexico.
Once you are in Mexico, it depends where you are flying. The only F will likely be on some flights with Aeromexico, and Interjet. I fly Interjet from time to time. Their inflight service is good, but some flights have baggage restrictions. Also, their main hub is Toluca, which wonīt help you if you are basing yourself near MEX. Iīve never flown F on flights in Mexico, since I live in PVR and we hub out of MEX which is only about an hour......and Aeromexico primarily uses smaller aircraft with no F on that run. I do fly F whenever I go to the U.S. and I would say that Delta or United probably have the best F, but no one offers an international style F to MEX.