Heat Suit
A plain sheet of metal over a lining of hide. It does one thing: lets you stand in the deep.
The suit you make before the Insulated Suit. It doesn't reduce the heat of The Deep, it stops it outright. It only spends charge while it's actually protecting you, at 3.6 a second, so wearing it on a green hillside costs nothing.
Top it up from Pack Cells on your back, or a Charging Pad.
Wearing any suit slows you to 88% speed, and your hands (mining, swinging) to 90%.