Wait, there is not temperature distinction between these three? So there is no difference between teplý/horký? I am browsing dictionaries and they consistently distinguish between chladný and studený… For instance SSČ says: "studený 1. mající nízkou teplotu, vyvolávající pocit zimy, velmi chladný" just as cold is very cool in English.
You're right, "chladný" is typically less cold than "studený" - especially when describing objects, food, drinks, or even character (where "chladný" means "unfeeling/reserved", not "cool").
The distinction is blurred when talking about the weather. Since "studeno" is rarely used here, "chladno" simply means cold (weather). Similarly, you don't usually say "It's cool outside" as it can easily be interpreted as something else than temperature. But you may say "It's chilly".
Even stronger words are "mrazivý/mrazivo" (in some contexts) - freezing cold, or "ledový" - ice cold (doesn't quite work as "ledovo"). So when describing a drink, we have a scale of: chladný-studený-ledový. For temperature (weather) we have roughly chladno-zima-mráz. It's hard to assign a 1:1 correspondence with English words.
I agree that I would usually translate "(venku) je chladno" as "It's chilly (outside)", and "(venku) je zima" as "It's cold (outside)". But these are nuances a different speakers might have different opinions.
Ok, lol, I thought you meant "baby" as in "little child".
As a term of endearment for an adult person, you certainly can't use "mimino". You can use "baby" (or "bejby") as a loanword or one of many similar Czech expressions such as "kotě" (literally kitten) or "brouku" (literally beetle, in vocative).