I dont think Jack is boring, but it is very popular.
If its too safe for your liking you could always use it as a nickname for any ‘john’ related name like Johan, Ivan, Jankin, Jenkin, Jackin, Jacque, Jonathan, Jackman, Jackson Jacob, Jacobi etc.
As for middle Id personally go with a longer name to help the flow a bit. like Jack Maxwell, Jack Thomas, Jack Nicholas etc.