Move #2: Beef up the bullpen
The bullpen has been a major focus this offseason once the starting rotation was filled out. Players such as Ryan Helsley, Giovanny Gallegos, JoJo Romero, and Andre Pallante figure to be the most prominent relievers next year, but John Mozeliak has stated on multiple occasions that he wants at least one more high-leverage arm to add to the bullpen before next season starts.
Recent reports have indicated that Mozeliak plans on finding these bullpen pieces via free agency, but he isn't completely closed off to the idea of using a trade to fill in the relief corp. There are a plethora of relievers that Mozeliak could find through free agency. Phil Maton has been rumored by Derrick Goold as a player of interest, but others such as Matt Moore, Matt Barnes, and Keynan Middleton all have high-leverage success.
As was previously stated, the Cardinals could also explore the trade route for relievers. Tyler O'Neill could net a decent reliever in return, but any one of Tommy Edman, Dylan Carlson, or a prospect the Cardinals have would be enticing for opposing teams. Justin Lawrence of the Colorado Rockies is an interesting reliever, and there are plenty of teams who don't intend on contending next year that could trade one of their relievers for a prospect or two.
Improving a bullpen that had the 23rd-worst ERA last year and the 24th-worst WHIP last year is imperative. Adding at least one bullpen arm, particularly one with high-leverage experience, would be ideal. Craig Kimbrel was signed for $13 million, so look for a deal similar to that if the Cardinals dip into free agency to fill this void.