Consider this comp of one-time All Star first basemen:
Over the past three seasons Wil Myers posted 4.0 bWAR in 393 games while Mitch Moreland posted 4.1 bWAR in 364 games.
Here are the 2020 Marcel projections for the 29-year-old Myers and the 34-year-old Moreland:
WM 479 PA, .244/.322/.444/.765, 58 R, 19 HR, 55 RBI, 24 2B, 2 3B, 13 SB, 47 BB, 143 K
MM 413 PA, .243/.320/.451/.771, 54 R, 17 HR, 61 RBI, 21 2B, 2 3B, 2 SB, 41 BB, 94 K
https://www.baseball-reference.com/players/m/myerswi01.shtml
https://www.baseball-reference.com/players/m/morelmi01.shtml
Of course the Red Sox would like to upgrade but that is a tall order if the Sox want to get under the luxury tax threshold.