It's always very good advice to make your reservations with the hotel directly whenever possible. Afterall, they know their property the very best. When one calls the toll free central reservations number they probably have never set foot at the property and are reading from a script about it.
I was a FOM (Front Office Manager) at a 4 Star Property earlier on in my Career. We could almost always track our dissatisfied guest issues to reservations booked through external sources. S/t their info isn't as accurate or up-to-date as calling the Property directly.
As others have mentioned you can ask to have an additional bed brought into the room. If you can request a "Murphy Bed" it is more like a bed on wheels as opposed to a cot. I wouldn't put anyone on a pull-out unless they were a young child. Just about every Adult who sleeps on a hotel pull-out complains about it at check-out. If only they had called the desk during their stay we could have done something about it.