Hey Akhilesh, You can follow this itinerary Day1 -Kochi sight seeing and Drive from Kochi to Munnar Day2-Munnar sight seeing Day3 -Drive from Munnar to Thekkady and Thekkady sight seeing Day4- Thekkady to Allepay and Allepay sight seeing Hope this helps.
If you are coming by flight, you can come to Calicut. Day 1- visit the city and its amazing beach and calicut is famous for its local food. Day 2- Then you can go to Wayanad, there are many places to camp in wayanad, which is famous for hills and climate. Day 3- You can then proceed to Munnar and Idukki, where hills are queens. You'd probably miss the 'Neelakurinji' flower season which bloom once in 12 years, the season is almost over. Day 4- Next day you can visit Aleppy, where you get astonishing view of backwaters, you can have a stay on a boat also i hope. Option 2
Come to Trivandrum and proceed in the order backwards. All places except Wayanad and Idukki have railway connection.
I visited Kerala 2 years back for exact same duration 4-5 days. My itinerary was :
Day 1: Drive from Cochin to Athirapally and visit Athirapally waterfalls.
Day 2: Drive from Athirapally to Alleppey and night stay in houseboat amidst charming backwaters.
Day 3: Drive from Alleppey to Thekkady. Explore around in the city. Visit spice gardens, attend Kalaripayattu and Kathakali shows and enjoy elephant shower.
Day 4: Jeep safari to the beautiful tea plantations in the morning and enjoy boating in Periyar Tiger Reserve in the evening.
Day 5: Drive back to Cochin. I enjoyed every bit of this trip and it was totally worth the visit. Feel free to ask any details in the comments. Happy Traveling!!