Advice please for my itinerary for my first trip to India (Kerala)

Hi everyone, glad I came across this forum - it's been really helpful!

My boyfriend and I are headed to Kerala in a couple of weeks. We're trying to prepare a rough itinerary taking into account the time we have (12 days) and the time of year (we've already experienced monsoon season in SE Asia and didn't have that much rain at all - should we expect worse in India? Also will there be things going on for Onam?)

Please comment as I'd really appreciate input from people who've actually been there and experienced it. The only thing that's already booked is the flight into and out of Cochin and a hotel there for the first 2 nights.

Day 1: Arrive in Cochin (early evening)
Day 2: Sightseeing in Cochin
Day 3: Leave Cochin for Munnar (what's the best way to make this trip?)
Day 4: Munnar
Day 5: Leave Munnar for Thekkady for Periyar wildlife sanctuary (is it best to stay overnight in Thekkady itself or in a town/village close by?)
Day 6: Periyar
Day 7: Leave Thekkady for the backwaters (haven't quite decided whether to rent a houseboat or just take a couple of short ferry rides - the houseboats look so luxurious but my boyfriend feels sick on boats! Plus we like mixing with the locals so maybe the second option is better.)
Days 8-12: Not figured out yet so suggestions please! Please tell me if it's worth going to down to Trivandrum. I've heard lovely things about the beaches of Kovalam and Varkala but maybe it's just not worth it in August? Or perhaps the beaches further north are just as good? Or would we be better off visiting a bit of Malabar (finishing backwaters tour back in Cochin then heading north)?

Sorry for all the questions! Thanks so much in advance!

Add one day to your stay in Cochin. The second day take a trip with the KTDC, see here, this is a good introduction to the backwaters.
We did the full day trip and found it very good.

After Thekkady take a bus to Kottayam and go with the local ferry to Alleppey. On your way you can observe the houseboats and decide if you like that, we did not.
Instead of that we hired a rowing boat for a day.

If you want to go to the Southern beaches the 8 hour boat trip from Alleppey to Kollam is another option.

Hello
Your itenary is nice. House boats are luxury even cheap too. There are some ....You have to bargain. WHy cant you look some places of water falls? a nice place ATHIRAPPILLY WATER falls around 80 KMs behind cochin north east side.. there is nice cottage too.

There are a lot events on ONAM FESTIVALS. Even our village too there is ! Do you like to join as a guest on stage?
Salutes
Bonjour

Thanks, that's a really good idea. :)

You may want to refer my trip report for few of your questions - My Kerala Trip

Regards,
Nishant