I recommend a roller shade gate. Here is an example.
https://retract-a-gate.com/
Be sure to check on the recall and safety track record of gates, sleeping products, swings, and chairs. Stay away from puffy, soft sleep products and kids sleeping in gear that's not intended for sleep (swings).
We tried small and large plastic walled playpens (no floor). They were not very effective and they were hideous.
My mom swore by the playpen she used with me and my sibling. We turned out fine but these mostly don't exist anymore because they were a safety hazard. We were also quiet sit and play type children.
If you will have two nappers, you may need two pack'n'plays and they can be used as temporary playpens up until a certain age (forget specifics). You need some kind of baby pen because nanny needs to have hands free to cook or to be able to answer the phone or use the bathroom.