Recently stayed at Theo's apartment on a return trip to Paris. I found it to be easily accessible from CDG airport—you can take the RER train directly from the airport and his apartment is a 5 minute walk from the Chatelet-Les Halles station.
The apartment is centrally located in the 1st and easily within walking distance of most of Paris, its main tourist attractions, cultural centers, restaurants, shopping and most iconic neighborhoods.

The apartment itself is well cared for, easily accessible thanks to an elevator and receives great light throughout the day. The futon bed is comfortable, bathroom functional and there is plenty of space—it's a studio but doesn't feel like it because of the separate kitchen and bathroom.

Theo was easy to reach via email and text message. The key exchange couldn't have been easier. Everything on this listing was exactly as pictured—no surprises.

Would definitely stay at this studio on a return trip to the city, and would recommend it to anyone looking for a safe, comfortable place in the heart of Paris from which to explore the City of Lights.