mesh collider - alternative mesh

i have a need for extensive use of mesh colliders in my game, i noticed significant drop in frame rate though. when using box, sphere or capsule colliders everything is fine, but they are not accurate. i can replace some of the mess colliders with primitive ones where i can but some definitely require mesh colliders, so my question is can i use alternative mesh collider? alternative mesh would be low poly of the high poly model that will be in the scene. is that possible?

if not what would you people propose?

Yes that's possible. In the mesh collider component you can choose any mesh in your assets to be used as the collider mesh.