As the heating element I used the carbon tape. It looks like a thin, soft cloth and not interfere in a bed.
The carbon tape can be sewed, but instead it can be simply glued. Because of this I did it in just 1 hour!
Under the carbon tape to put iron-on hemming web tape.
Gently press the carbon tape with an iron that is stuck to the fabric.
Squeeze between two layers of carbon tape some silver from the syringe, insert the bare wire, squeeze glue place until the glue is completely dry.
Cover with second piece of cloth and gently press the iron over the whole area.