Sedioso Large Cat Carrier for 2 Cats, 21.7X 13.8X 13.8in Pet Carrier for Cat and Dog Up to 38lbs, All-Sided Mesh Cat Carriers with Great Ventilation, Portable Soft Sided Pet Carriers for Traveling

This is what I use. You can remove the divider and there's plenty of room for one big Maine Coon. It leaves plenty of room for them to spread out and move around. https://www.amazon.com/dp/B0CLH7M92V