Oh puh-lease >_>
Sorry to inform the devs, but you don't need to lie down to have sexual intercourse. Players have RP'ed that kind of thing with all kinds of very obvious poses already, lying down won't change ANYTHING. Those who want to do it are already doing it. Those who don't want to (the overwhelming majority!) are not gonna suddenly start rolling around on the ground with each other just because they can decide where to sleep now.

Oh, and since we are on topic already - can we also please have actual SLEEPING poses for female Miqo'te, Elezen, etc.? I think my Miqo'te's spine has a crack already and my Elezen's neck is so stiff, even when she is awake and standing, it's bent weirdly.