Kochi is also a very nice city, but if you're coming from Shimla or even Delhi you're going to find it sweltering hot probably. It's about 26⁰C (80⁰F) right now... (I'm close to Kochi and honestly in these temperatures it doesn't even feel like Christmas)

Ps, Kochi can be quite bustling. The more remote and rural towns (like Munnar) are a relatively safer bet.