By homesteading principle - one has private property rights to anything they homestead. The body is the first thing a person homesteads. Then comes products of their own labor. The notion of private property includes the right to exchange your property with others. Of rent it to others on some terms. And here we already have a moral case for prostitution - one exchanges some goods for "renting" somebody else's body for sex. That is prostitution based on the first principles!