How best to fill a nook with a large couch

We just purchased a house and there's a small room with a 7'1" by 4'6" nook that we'd like to fill with an extra-deep couch and use for TV watching. There are a few couches we saw that we like (for example) but we also have to fit them through a 2'6" doorway at the end of a staircase.

How do we search for a couch based on these nontraditional dimensions needing to separate it into 2 pieces? Or do we just need to buy a custom couch?

Thanks for any help!

Big sofas won't go through little doors unless they are designed to assemble in the room. Here's one maker you can try:

https://www.simplicitysofas.com/