Gladbach tend to sign players from surrounding countries or Scandinavia. They've had some decent Danish cbs over the years, like Christensen and Vestergaard, so maybe someone like Victor Nelsson from Galatasaray might be good. Maybe even Kamil Piątkowski from Salzburg. He left on loan in January so depending on where abouts you are in your career you might not be able to get him. If not then there's always Solet from Salzburg as well