Logical me says build your own door any size you need. All they are to build is DIY or find a carpenter friend. Build a large frame out of wood, like a picture or mirror frame, and put a cross in it, then staple some chicken wire on it. You could even paint the wire to match your decor. Or put artificial flowers in it...Make the frame any size tall you wish. Instant x-pen. A room divider might work too!
Now that you have the door you can fasten it by simple hinges to any existing door frame to keep him in that room or part of the house. You could really get creative with this....Wow, wish I needed one!
Or you could buy a screen door and make it match your decor. Where there is a will, there is a way.