Custom collider for procedurally generated tiles

I am currently working on creating procedurally generated islands using Perlin noise and 3d blocks/tiles. I have already managed to create different sized islands, but my problem now is how to deal with collisions. The easy answer is to give a box collider to each tile, but since these islands are made of hundreds or thousands of tiles the game would be unplayable. My idea was to create a custom collider using the dimensions of the island and have just one collider per island (as shown in the picture). However I haven’t found any information on how this could be done, or if there’s another (better) solution that I haven’t thought of. Any help would be appreciated.

Thanks in advance.

Add Composite collider