Scoring runs. I think everyone agrees that the Sox offense is putrid. There will need to be at the minimum at least 3 offensive upgrades. I doubt the Sox trade Rafaela or Anthony, they could trade Contreras but then you're counting on Casas as the free agent class is trash. SS will be manned by Story at least the first couple of months and the hopefully replaced by Arias. Catcher needs an obvious upgrade and I would assume the Red Sox will be in on Jeffers but so will several other teams. That leaves 2b/3b, I could be wrong but I doubt they move Mayer for pennies on the dollar when his ceiling is so high.
This is a personal opinion, but I don't value defense at the corner positions. Abreu has a league average bat and plays solid defense, belongs nowhere near the middle of the lineup. Durbin is similar to Abreu as most his value comes from defense, but the offensive upside is limited as he just doesn't hit the ball hard(4th percentile exit velocity), even in his current hot streak his xwOBA is only .299 where league average is .320.
Early would be my choice if I had to move at pitcher in a package for a upgrade position player, I think Tolle and Bennet are significantly better and Eyenson will be in AAA next year with couple of other interesting arms.
None of Durbin, Abreu, or Early alone will bring back an impact bat, but maybe if they are part of a package.
I think a lot of fans including myself get caught up getting the most value out of players, when the goal should just to be able just to get the best players.