medieval & language dweebery

While trying to make a funny joke in response to my friend's comment that if the money runs low, she might work as a sword for hire, I pointed out that Doppelsöldner get hazard pay, and Emperor Maximillian lets his landsknechts dress any way they want.

My German's rusty, so I'm now confused whether the singular is Doppelsoldat, or whether Doppelsöldner is both singlar and plural. I don't believe (der) Soldat has ever had a distinct female (I think it might be implied), otherwise I think I may have been one of the first people in history to use the term (die) Doppelsöldnerin.