Based on your likes, if u want see greenery, you can visit munnar, wayanad. If u want beach experience then you can visit varkala and muzhapilangad driving beach.
There are many places including Varkala, Ponmudi, Thenmala, Wayanad, Munnar, Wagamon, Fort Kochi, etc.
For reference, you can use recently published "Kerala Tourism" app. It is an official application by Kerala Tourism Department, which shows various tourist places all over Kerala.
This article should help you make up your mind on which places in Kerala to visit as a solo traveler:
https://www.tripoto.com/kerala/trips/kerala-tourist-places-luxury-holidays
If you are a budget traveler ignore the luxury stay recommendations. Hope this helps!
Happy traveling. Regards, Senneil