Let the mattress air dry completely before putting sheets back on. Put a fan on it or open a window. A slightly damp mattress is a breeding ground for mildew, and mildew smells like regret.
Once it’s dry, consider buying a mattress protector. That waterproof cover should have been there from day one, but hey, hindsight is 20/20 and vomit is always 3 AM.
You survived. You are a cleaner of messes, a warrior of the night. And next time your kid coughs weirdly in the dark, you’ll have a plan. And a box of baking soda under the bed. You’ve got this.