Hi you can cover places in cochin like Fort Kochi which is a major tourist spot. Then i would suggest Munnar where iravukalam national park, Anamudi, Tea plantations, Top Station etc are major attractions. Then you can proceed to Thekkady where Periyar Tiger Reserve, Boating, Jeep Safari, Sathram etc are major places to cover. After that kumarakom where you can pay visit to kumarakom bird sanctuary and also include , Aleppey which is famous for house boat. If you time you can include kovalam beach, poovar islands etc in trivandrum. Happy Journey.
Travel your own i suggest. Kerala is tourist friendly state. * One night stay at cochin and explore Marine drive & fort kochi. * Plan 2 days stay at aleppy, which is only 45 minutes train journey from cochin. Stay one night at a resort and other night in the house boat. Most of the resorts run houseboat facility too, so u can book both at once.
* travel to munnar. I would suggest overnight travel in bus. Book for a tree house stay. It is mindblowing experience. There are many hotels with tree house. If you like adventure sport, stay for 2 days and spend a day for adventure activities.