Box/mesh collider problems

When I insert a 3D model concave or "open" and insert the box collider I created a collider is not suitable to model



as you can see is covered by the collider also the part near the backrest, and that's not good for my game.
I tried to insert the mesh collider but unfortunately are not created the collider among others 3D models as they contain too many triangles. (in my game, the models can be moved, so it is important to have a precise collider).
What can I do to fix it?

 

you could make a very low poly mesh that represents the chairs basic shape and use that for your collider or you couls use two box colliders and position them on the chair

 

I solved it.
The only solution is to place each piece individually box collider.

So we put a lot more time but for the moment it is the only solution

 

You could use a mesh collider and use a very low poly mesh of the chair. It's not to much of a problem with the chair but if you had something like a cup, mug or donut then you could be better off with a mesh collider and very low poly model.

If you don't need things to be able to go under the chair you could reduce it to two colliders.

Mind you it would be nice if Unity added the ability to build low poly colliders from meshes automatically or ideally with user input to set LOD levels.