How do I render a mesh below everything even if it has other meshes above it?

Im making an isometric game.
This requires sprites to visually go behind and forwarded as needed.
Though the floor is necessary to stay in place so that the 3D character can walk in it, and cast shadow into it.
Though if i need some buildings to go below, they will be cut by the floor.

This is what happens if i need the sprite to be a bit more below in the Y sorting^, which will be necessary in some cases.

I dont know how this is solved in isometric games but i assume the floor must go below everything and rendered last even if it has stuff on top of it.

I tried using a technique i saw posted, that is to set the material to Translucent and then Disable Depth Test. This kind of works, but it needs all meshes to have this in the material except the floor, and that sucks. And it also disables all the shadows…

So what should i do?
How can i make the floor always render below everything regardless?
If not rendering the floor below everything then what should be done in this situation?