Hi Sam - think it was me that turned you on to centreparis.com, but as I noted I have not used them myself. Which apartment are you considering and where would you have to pick up the keys - is it far from the apartment? Also, I prefer to have someone meet me at the apartment to make sure all is in order on arrival. Would you also have to return the keys to an office rather than leave in the apartment? That could be a pain at departure time.
Have you also checked on www.homelidays.com? They list some reasonably priced places that may suit - e.g., property 191106 looks like it would work and is in a decent location, may even be able to take the Air France bus from CDG to Gare de Lyon and walk from there.
What are the dates you need the place in Paris?