I would say a do it yourself trip to locations which are nearby is more advisable. Agreed a package tour is peace of mind, however, a properly worked out do it research will give you the flexibility as well as the fun that you want. It also invariably allows you to get the best flight deals, best hotel deals, and best sight seeing deals, as you can then book each of these separately from sites which offer you the best deal in each of these. For the itinerary, look up the itinerary on 2 or 3 of the big tour operators, you will notice a lot of overlap, now plan visiting thsoe places yourself. You can do this by either
booking a cab, or signing up for one of the half (usually best choice), or full day tours. If you are interested in a DIY trip, these are the sites I would recommend based on my experience with getting good deals. Note there might be other sites too, but these are usually the most consistent in terms of good deals.
Flights:
Cleartrip, Ezeego, Yatra
Hotels:
Travelguru, Hotels.com,
Agoda
Sight seeing: AsiaTravel
EDIT: Since you seem to be in Chennai, do check out the websites of Air Asia and Tiger Direct. They usually have great early bird booking deals.
Trip Advisor.com website and forum are great for research
lonely planet is another good source for research.
and i agree...half the fun of the trip is in planning