Wolves defender Danny Batth is a product of the Wolves Academy and has made more than 200 appearances for the club. He was club captain and helped take Wolves back into the Championship in 2014 and lift the Championship title last season.
Millwall midfielder George Saville had been linked with a permanent transfer to Boro during the summer transfer window, however a deal failed to materialise. He joins Boro having scored 10 goals for Millwall during the the 2017/18 season.
The deal for Saville is thought to include a £8m permanent deal when the transfer window reopens January. That would be a club record fee for a Millwall player.
The Northern Ireland international has five caps, having made his debut in October 2017.