Your best bet would be cocoa butter, it'll help set the item firmer. But regardless, coconut oil and chocolate make a meltaway candy, which is has a low melting point, hence it easily melts away when eaten. Another factor would be if the chocolate and cocoa butter is in temper. If you melt your coconut oil, chocolate, and additional cocoa butter and just pour it into a pan or frame, it will take a very long time to set, and when it does, will be very soft. However, if you take that same mixture and, once melted and combined, you pour it onto a stone slab and temper the mixture, it will set faster and firmer. What exactly is the raw cocoa product your using? Does it contain sugar?