Covering firebox floor

[tgbrew]

Hi All,
We have a piece of slate covering our old ashpit in our fireplace but it isn’t quite big enough for our grate to fit on. We made it work last year but we want a more permanent solution.
What material can we use to cover the entire bottom of our fireplace? Is there a certain stone that would work in that heat? Or try to pour cement/mortar somehow to make a new floor? I’m not sure that slate is the best choice and any/all advice is appreciated.

 

[pen]

lay down firebrick?

How about a pic of your setup? Seeing the situation might help spawn ideas.

 

[tgbrew]

Interesting point on the fire brick. We have angles so not sure how that would work. Could I DIY it? I tried to post a pic below. You can see the slate on the bottom but it is a little camouflage.