Let me tell u my plan for Kerala from 20th Dec.
Hope it helps ur plans.. 1) Kochi Get down at ERS (South station)
Hotel
Historical fort Cochin / Bastion bungalow - 7 km from South Railway station Dutch palace / Mattancherry palace - 5 from fort
Night stay
2)
Travel to Munnar - 150km / 4 hrs
Hotel
Mattupetty dam - 15km / 30 min
Echo point - 7km / 20 min from dam
Kundla lake - 8km / 20 min from point
Come back to Munnar - 30km / 1hr
Eravikulam National park ( Raja Malai) - 12km / 25min
Night stay
3)
Travel to Thekkady - 90km / 3:30 hrs
Hotel
Kathakali show (optional)
Spice plantation visit
Elephant ride (400Rs)
Periyar lake (It's boat ride)
Night stay
4) Travel to Alleppey - 130km / 3:30 hrs
Check in boat house by 12 noon (important) ( It's start time for boat house, as I know now)
Traveling till evening 5 and stay overnight If not interested in stay, only for ride (400Rs for 2hrs)
5)
Travel towards Kochi from Alleppey - 60km / 1hr Yet to research few other places. Enjoy your trip. Hope it helps ur plan. :)