The Red Sox have some decisions to make regarding the left side of the infield. 3rd base in particular has been a problem, at least on the offensive side of the ball. Since the start of last season, the Red Sox have gotten a slash of .247/.303/.366 according to Over the Monster. It seems like WIll Middlebrooks' days in Boston are numbered - the Red Sox have been loosely connected with a number of 3rd baseman, i.e. Pablo Sandoval, Pedro Alvarez and Chase Headly. That probably doesn't inspire a whole lot of confidence in Middlebrooks, but I don't think most Sox fans view him as the 3rd baseman of the future.
I don't think the Sox don't have to go out and spend a ton of money bringing in a 3rd baseman. Brock Holt came up as a 3rd baseman, but was shifted around the outfield for most of the year, but there's also Xander Bogaerts as well. Bogaerts has some experience at 3rd, having played 3rd for most of his time last season, including the postseason. So could the Sox move Xander back to 3rd? It's definitely possible, but given the wealth of up-and-coming talent (i.e. Garin Cecchini). Holt is best employed as a utility man and that means a hole at shortstop. So, who plays shortstop then? Mookie Betts could be a possibility. He was originally a 2nd baseman, but the Sox had him play outfield so they could get him up sooner. But 2nd base obviously isn't an option once next year rolls around, and it doesn't seem likely that he'll get much playing time in the outfield with Yoenis Cespedes locked up through next season and Rusney Castillo signed for 7 years and the Red Sox scouting another Cuban defector, Yasami Tomasi. Betts'best bet may be to learn how to play short as well.
While a guy like Sandoval could be an attractive option, I don't think the solution to the left side conundrum comes from the outside. The Sox could end up having Garin Cecchini at 3rd and Bogaerts at SS or Holt as a full-time 3rd baseman, or they could move Xander over to 3rd, provided he works on his defense in the offseason. Wherever Xander plays next year, his defense HAS to get better. The point is, I think any of these guys could be a viable solution to the problem and the Sox don't necessarily have to bring in help from the outside.