Ooops, bought a granite slab as a base for my new grill

Hello ... longtime lurker, first post.

I bought a grill from Engelbrecht, it's one of those Argentine or Santa Maria style grills where you can raise and lower the grate with a flywheel. This particular grill doesn't have a metal firebox to hold the coals - the bottom is just empty, so that you can place it directly on the ground and build a fire right there on the earth. Hardwood or charcoal, they both work.

I had a plan to place it on a DIY table of sorts, to bring it up to a more comfortable height. For this purpose I bought a big slab of granite that I hoped to place on cinder blocks. My original plan was to add a base of fire brick directly on the granite, and place the grill on the fire brick, building the fire right on the fire brick base. Then I learned that granite can easily crack/break/explode when exposed to high heat. And also that fire brick doesn't insulate much at all. With this plan, the granite will likely get very hot and crack sooner or later.

So, my options? I could purchase additional insulation, like ceramic fiber blocks, to place between the fire brick and the granite. But I have no idea how thick would be safe. Or I could forget about the granite slab and pour my own concrete slab as a base ... with possibly an additional slab of refractory cement? And possibly also additional insulation?

Basically it's become rapidly clear that I have no idea what I'm doing when it comes to all this stuff.

Any advice is much appreciated.

I have seen Granite exploding at a fire pit we made. Luckily nobody got hurt but the "Bang" it made was not from bad parents.
The entire bonfire was cleared out and glowing wood pieces were laying around in a radius of 30 ft.

So Granite is for me a no go, especially if it gets wet inside after a period of humid weather.

To isolate a concrete BBQ I took a 1" layer of white sand and Red Clay Bricks on top.
The bricks I later changed for red clay tiles.
The concrete still got too warm to tough after 12 hrs. pizza fire, but not glowing hot so I assume 2" white sand with clay Tiles or Bricks could isolate the Granite.
But I cannot guarantee this, you need to try yourself.