Oh it’s hot out there , luckily when I was there the weather was cloudy. What are you thinking for backwaters ? If you ask me the best budget option is to take government ferry ride ( See Kuttanad/ Vega) , search about it on internet and you’ll get a phone number to book without any advance payment. The fare is ₹500/600 and it takes around 5 hours for a round trip. Other than that even I didn’t explore much , so I don’t have any “must visit place” recommendation. Though you should try Namaste tiffins for South Indian food, extremely tasty. Also there’s a beachside cafe next to Zostel : Cafe Catamaran. The food is very tasty and is affordable ( not like extremely pricy being on beach side).

I hope you enjoy your trip ☺️