What I do is give them a $5 to $50 allowance and put them under the tutelage of an educator. In a couple of game days, they are ready and willing. Work on your MC's Charisma also. I can usually have even a slave or hired female with the worst traits, like a feminist, carrying children in the first game week. I personally think it is too easy and probably needs to be harder. If you can't get your satisfaction from your slaves or female companions, then just go see a working girl at one of the inns or bars. You can try different things, even books can help. The mechanic is really not to hard to grasp if you are trying to groom them for specific roles.