The pressure isnt violently different (it’s only 1atm. Scuba divers can go up to 70atm with special breathing equipment). The issue is the boiling point of water is very low at that pressure, but on a cellular level the physics of that are going to be different.

Also space being “cold” is a bit of a misconception. Your body produces heat constantly, and it’s hard to dissipate heat in space, since you can basically only radiate it out as infrared light, which is a much slower process than being in physical contact with something.

In fact, we use vacuum chambers to insulate things such as in those metal thermoses that they tell you not to put in the dishwasher.

So being in space would actually be more like being wrapped in the thickest possible blanket than being cold.