Still there is a lot to take in account.
For space, let's see: the player will lose heat to space mainly by radiation. We would have to simplify this a lot, such as: considering a human being is made of around 70% water, let's make it a round ball of water. Also, this ball of water is in thermodynamical equilibrium at every timestep, that is, the temperature is always equal in the whole body of the player at any given time. Also, the player exchanges heat only by radiation and emits it spherically as a point, obeying Planck's law for a blackbody (this is a "formula" developed by Planck for a blackbody, which is a body that emits the largest amount of energy than any other at the same temperature). Then we would have to make an energy balance, which is basically the formula you put in there.
Even though there is a lot of simplifications involved the analysis I just made and it is probably not hard to implement in your code, you must know some physics to understand everything and this is just for one level (and space is probably the easiest one to model). Even though I have no experience in game design, I don't think the analysis I just made would be much more accurate than an intuitive and simple formula, such as "I believe the player will lose about 10 degrees Celsius in 7 seconds" and adjusting as you wish.
However, if you want to model everything physically, I believe that you should either have someone who knows physics to work with you (if you don't know, of course) or start digging into physics textbooks, specially thermodynamics (which will probably take much longer, but you'll gain knowledge).