I don’t know where you live. But where I live, styrofoam costs next to nothing. In fact, you get it for free, if you don’t mind looking through another man’s trash. You can also probably get some for free if you ask a company, that gets stuff sent, that need cooling. Like a supermarket.

For environment: styrofoam is a kind of plastic, so there is that. On the plus side, it’s quite little plastic inflated with air.

I assume it’s way better than getting a replacement fridge, especially considering the electronics and maybe the coolant gas (I don’t know if that’s still an issue).

I wouldn’t be surprised if the electricity saved alone offsets the environment damage (assuming not fully green power used to run the fridge).