Go to the CDG Marriott's website and see if they have a shuttle bus which will pick you up at the terminal. I always stay at Marriotts worldwide and always check there first before arranging a driver or taxi.
We have used Viator in Paris(and other cities) and have found them to be good quality...not as good as Tauck, but then that's a pretty high standard to live up to.( www.viator.com)
Viator does a nice job and gets you to the front of the line in a lot of places. We used them for Versailles and the Eiffel Tower dinner and bateau mouche river cruise and were happy with both. So much to see in just a day and a half!