Venting chimney breast

[Sausage Sandwich]

Hi all,
I'm planning on blocking the chimney breast in the living room. It's been capped at the pot but theres just a open chimney breast and it looks ridiculous.
My plan is to put some therma fleece insulation in the opening, mount some tile backer board to cover the opening and then tile to match the surounding pre existing tile.
I understand i have to vent, i was thinking something not too big liek this https://www.screwfix.com/p/map-vent-fixed-louvre-with-flyscreen-vent-brown-229mm-x-76mm/158hy

Would this be suitable, and how do i maintain the air gap behind the vent from being covered by insulation?
Thanks.

 

[foxhole]

You don’t insulate , serves no purpose .