Basically that would be called a catsuit and they can be made out of any material you like.
Also, you could check out websites that cater to military, fire fighters, medics etc as they have all types of colors and clothing to work in all types of weather. Gall's is a big one...
A standard you could use is to go buy a set of Dickie's pant and shirt combo as they have several colors available and they will match. Just buy your size and if needed, you could always sew in a piece of eleastic to the inside to make the material hug you closer if you like. A trick you could do with the heat is modify your undersuit by adding in mesh areas. Cut out a section of cloth in a non-support area or such, and sew in a piece of mesh fabric in the same color to, in essence create vents. You will see all sorts of tropical adventure / hunting shirts pants and gear that have built in vents sewn in to help with airflow and drying out after doing river crossings. When using the two piece undersuit, you will have belts and such that will go around your waist and will hide the joining of the two. I use a grey set of Dickie's work pants and long sleeve shirt as my undersuit. With all the gear on, you can't tell it's not a one piece.
Another option is one that I have been considering is building what the military calls a "cool vest" or "microclimate" vest which would go under your armor and is attached to a small blower motor that circulates air next to your body and helps with heat dissipation. I run hot all the time and get hot easily, I am going to have to mod my helmet with a battery powered fan before this summer to help, and will be looking into the air vest again soon...still haven't got it all figured out, but am getting there.
Good hunting.
Ajax.
