I have a wire crate that is 18Lx12Wx14H and it seems a perfect size for a yorkie.
I bought it for potty training but ended up not needing it for that. I lucked out with this new puppy & didn't need to use it for potty training because I set up a playpen with bed & pee pads and she used the pads each time. Then when I took the playpen away, she still used the pee pads. I reward her each & every time she goes on her pads when I am home to see it. I swear she'll hold it while I'm gone so she can pee 5 times in my first hour home to get five treats