Cold x Chilly x Cool: Qual a diferença?

As slang, "cool" dates from the 1950s or so, and although it is still used today, it rather dates a person. A younger person might say "rad", as an example. The context helps. "That's really cool" or "that's cool" as an approbation is a common way to use it.
If you add "totally" you might appear a bit more modern, as "totally" is "Valley Girl speak" from a more recent era, and originated in California. I do hear "totally cool" now and then.
"laid-back" means "relaxed" and isn't quite the same as "cool", which means "good" or "of the moment".