What kind of pup do you have? Anything that you get; you want it to be scalable for the pup once it grows up.
Don't laugh, but a plastic milk crate bungee'ed to the passenger handrails with a cushion underneath; with a short leash to keep the pup from jumping out may work for you at the moment (temporarily).... very to take man's best friend for a motorcycle ride.
Only a motorcyclist knows why a dog hangs it's head out of a car window...
Lot's of ideas here:
https://www.google.com/search?q=dog+...qS7R-psqiB0rM: