Sons bedroom opens to stairs

New mom here. We are building a second bedroom for our son. It will be done when he’s 2 1/2 years old. His bedroom door will open to a landing and a flight of stairs going up and one going down. Our bedroom and the living area is up the flight of stairs. Our father in law told us that he’s worried because he’ll have nightmares at that age and want to crawl in our bed which means he’d have to climb a flight of stairs. I thought we could just lock his door from the outside and have a camera there we can always watch. Any suggestions? I don’t know how it is at that age. Don’t need anyone telling us to not have his bedroom there. It’s our only option but I won’t get into that. Just suggestions for how to manage this situation thanks!