I’ve done a little research into heating elements. As stated in the book ‘Pysical computing’ the firm Minco has a wide range of heat sensors and elements. Interesting are the flexible sensors and elements. Both come in very small sizes. The sensors can measure very small temperature differences, I’ll seen numbers like 0,04C.
Here’s an example: Polyimide (Kapton®) Thermofoil™ Heaters
Polyimide Thermofoil flexible heaters, or Kapton heaters, are ideal for applications with space and weight limitations, or where the heater will be exposed to vacuum, oil, or chemicals. These thin, flexible heaters are rugged, accurate and reliable.
In the Netherlands the firm Alflex deals in these products. I couldn’t find any reference to the wearability of these products. Neither can I find any information on prices.