I assume that's Meiko in your avatar...what an adorable puppy! I clicked on your profile hoping to see more pictures of that little guy. Soooo cute!
Anyway, to answer your question. I suggest getting the 48" crate and blocking half of if off for now.
Mac - 4 year old GSD
Bart - 9ish year old GSD/Akita
& 3 Cats Buffy, Rusty & Magoo