If you want to get a feel for the Holloway area, which maybe more useful than staying in the Kings Cross area, there is a Travelodge under a 20 minute walk away from the university campus at Finsbury Park - Isledon Road. Travelodge is a chain of no frills hotels - clean and comfortable, but breakfast is extra.
It’s an expensive residential area, so any boutique hotel or B&B will be £££.
As others have said, the underground service is good, which gives you more options.
Ensure that any booking is flexible. France is way behind the U.K. in vaccinating its population and travel may or may not be permitted. The U.K. population won’t have all had their second vaccine until November.
In the U.K., schools are for the under 18s and university students wouldn’t appreciate be called school students!