Simple suggestion: You know how Ori will sometimes prompt you to mate with them? I think that chance increases if it's been a while, or if you're cuddled/made out with them for a while and declined their last attempt, leaving them pent up.
I think it'd be nice to give that mechanic, such as it is, to the other spirits. Spirits who are willing to mate with you will sometimes proposition you by themselves when you Chat with them. Or, with the introduction of having them invite you to their huts, offer to mate after inviting you over to their place.
Re-using existing systems in new places seems like a much more reasonable suggestion to me!