What's a synergy? A synergy is a combination of essential oils without carrier oil added. Once the carrier is added it's a blend. I know YL calls their undiluted blends BLENDS but this is just not to confuse non-industry people about what they are getting in a bottle as most won't know what synergy means, but blend is pretty understandable. However, I think you guys totally get this difference and may find it of interest to know the aromatherapy terms, so technically, these combos are synergies!
Ok, so let's make a synergy. Always use glass. I like 1oz glass droppers because I don't want to have a blend sit too long and I say blend b/c I'm adding carrier oil to dilute in there. So, you have your 1oz bottle and 15 drops is fairly standard for a synergy to which you're going to fill up the rest of the way with carrier and apply to the skin, although feel free to dial that back if you've got some serious oils in there like Oregano for example. If you're just wanting to make a synergy for use in the diffuser, then you'd want to, for example, create a synergy of 100 drops in a 5ml glass bottle (great way to reuse those YL empties), then re-label.
So, just make a synergy of Lavender and Stress Away. Now Stress Away is already a synergy of Lavender, Cedarwood, Copaiba, Lime, Ocotea, Vanilla and others, and while these types of pre-made combos created by YL are meant to stand on their own (so don't blend blends/synergies together or it will be absolutely overwhelming), I like to customize my YL blends/synergies sometimes to meet my specific needs. But you see how I'm using a single (Lavender) in the synergy that's already in the StressAway? That way, I'm not adding anything to the StressAway that isn't already in there. So it won't mess with the therapeutic benefits or confuse the synergy and be too overwhelming for me to smell, apply or inhale. I'm just customizing the StressAway, really.
I'll want about 15 drops in the 1oz bottle total for a topical synergy so I would probably do 7 drops StressAway and 8 drops Lavender but first SMELL IT, then if I like it, I will fill the rest of the bottle with carrier oil of my choice (YL V-6 oil, Grape Seed, Almond, Avocado, Fractionated Coconut, which doesn't solidify, etc.). If I'd like more Lavender to come through I would just add a couple more drops and smell again, then I'd smell, then I'd add the carrier once I was happy! Leave some room at the top (the neck of the dropper bottle) empty so the dropper can fit without overflowing your oil! Then I would use on my pulse points at night. If I'm making a synergy for my diffuser and therefore not adding carrier oil, I would take my 5ml bottle and add 50 drops StressAway, 50 Drops Lavender. Boom. Now that will sit next to my diffuser for night time awesomeness!
Now you make a synergy. The best way to start is to smell those 3-5 oils together to see how it smells together and consider adding more drops of the less prominent ones, and less drops of the stronger ones so they are balanced in the aroma. And let me know how it turns out!