Vanilla is one of the easiest notes to layer. It works with amber, musk, tobacco, tonka bean, caramel and soft woods. The risk is making the result too sweet, so balance it with clean or woody notes.
Simple rule
Choose one fragrance as the main character and one as the supporting layer. If both scents are loud, reduce sprays. If both are soft, use a stronger base note such as amber, woods or musk.