Where do you keep and use shampoo bars (solid shampoos)?

Would it be best to use a soap holder?

I'm currently using it placed on a slightly coarse sponge, but it's getting too soft.

The surface touching the sponge is turning into cream.

Is it unavoidable since it's summer?

It’s gotten so soft that I’m upset because I think I’ll have to throw it away even though there’s still a lot left.