Hi Sonia, you can book these tours with various private travel organiser but pondytourism seems a reliable source and i would suggest you to go ahead with it.
In pondycherry, u don't need any tourism to b booked as u can go urself as only u have places like beach, vinayaka temple, aurobindo ashram n local market all r nearby n walkable. and only auroville is 15 kms far from city.... but more than a day is enough fr it....