I would call customer service and see if they can help. They may be ale to book this for you .

Yes, hotels in Europe will "kick you out" if you just show up with what is basically a third adult. The rooms are just much smaller. My room in Rome had two twin beds and MAYBE thay could have squeezed in a rollaway, but... it would have been tight.

Others have reported being charged LOTS of money for the "required" upgrade when they attempted the just show up with the extra person.