Can you pressure cook whole fish and get soft bones without overcooking fish?
Here is the answer to a related question: How to cook a fish to make it's bones soft

Basically, the pressure cooking doesn't allow any moisture to escape the system so the fish will retain the moisture and not dry out. It will still reach a hot temperature inside the can, which may result in a slightly different texture than if you were to sous vide, for example. But the pressure cooking should soften the bones and be the solution you are looking for.