We'd originaly booked the ibis budget (reviewed here already) & saw the Montmorency on our walk to la Cite for diner, checked it out online & booked between courses - you check in at the sister hotel (which is really nice but twice the price)...More
"We stayed in the annex which had spacious rooms. I didn't see the rooms in the original building."
"Go for the cheaper sister hotel and have a little walk before breakfast"
"The stair is curving and tight. Consider your luggage when booking."