I bought a small crate that had an optional divider to adjust as my puppy grew. Without the divider, it was too spacious. It worked out really well. I can't remember the exact dimension...will have to get back to you.
The one I used is by MidWest and has two doors, plus the divider:
https://www.amazon.com/MidWest-Stage...0002TKBUS?th=1