Can't get around the water issue. We are made mostly of water. However, maybe through some external means maybe we can prevent the water from “freezing” well below 0c. As an example: one way to do this is to add salt which changes it transition point.
Anyway, what is the goal here? The goal is to slow down the metabolism of a the human being for a very long period of time without damage or side effects. What is the minimal external supplied energy (heat, food, etc) to keep the bodily functions operating properly. Also, what about atrophy and bone density (especially in a low gravity environment).
Anyway, it seems like you might be able to apply an external EM source that might suspend the the water molecules thus preventing freezing crystalization.
As I said, adding antifreeze can lower the actual freezing temperature of water. Eventually water must freeze, however. And when it does it forms a crystalline structure that is larger in volume than in the liquid state. Most substances shrink in size during solidification. Just about all metals, for example.
But what does freezing do to preserve something? Heat causes molecules to jiggle and drift around, eventually losing any of their original structure. So the colder the better. How cold can water get before freezing? Who knows. Without some extreme future or alien technology, not very far below 0 degrees Celsius.