Making your own tools is always more effective magically because you have put your own energy into the object, gave birth to it in a way. If the Oak tree spoke to you then there is a reason. As LG said, fertility isn't just babies, it's the continuation of life, nature. That's one of the reasons Oak is so magically powerful. As for the crystals, I've never been big into wands but most of what I have seen for sale seems more like "show & tell" or little kids stuff. I have met some people who added ribbons, carvings, crystals, etc to their wands but each had a purpose & most of the time these wands were reserved for "special occasions" their everyday wand was almost always much simpler.