You should know me better Lil. Singular is 'cozy' and plural is 'cozies'. I never wrote 'cozie'.
We don't use "Z". It wouuld be tea cosy and tea cosies.
"Cosy" as in warm and snug.
Tea cosies are traditionally knitted, or crocheted to cover traditional teapots to keep the tea pots and therefore the tea within warm.
Disclaimer
No "Z"'s have ever been harmed or damaged in the use of the phrase "cosy".
Methinks you're trying to be a little too clever there matey.
Gonna try to teach my granny to suck eggs next?