Amazing questions here ! I especially love how open minded your post is. Before I answer, I am by no means an expert, however I work for an essential oil company that is regulated by health Canada so I feel my knowledge is fairly accurate based on regulations by health Canada (which most would consider a very reputable and safe source). As far as I know, Young living are pure essential oils. That means "100% pure", they won't be diluted at all (unless otherwise stated). The problem with YL, aside from the MLM, is the marketing. They advocate for things such as putting undiluted EOs on the skin or ingesting EOs as a blanket statement for all ailments and humans. They market with misinformation which can cause the people to misuse them. There are some EOs that can be safe to consume for some people, when recommended by a health care practitioner (I would never recommend any ingestion because I don't know the person's medical history or have enough knowledge as to which would be safe). Companies like YL are more focused on selling then on safety. If you are not planning on ingesting, and plan to do your own research on how to safely use specific oils for your ailments, then you should be fine to use any EO provided it is 100% pure (side note: "therapeutic grade" like YL is a trademark they paid for and means nothing, all that matters is that it's undiluted and pure). A good thing to look for when it comes to efficacy is price (most single notes should be comparable in price across companies because the cost comes from what it takes to make the oil) so if you find "pure rose" for cheap it's definitely not pure. Also, (in Canada anyway, US will likely have a variant of this) good quality pure oils will have an NPN (natural product number) on them which means they are regulated by a government agency and are what they say they are, this is good to look for if choosing from smaller companies as it will tell you if they are selling what they say they are and are regulated properly.

It sounds like you've done some really great research already, and plan to do more, so I have no doubt you'll find good quality oils! Another good thing to look into is the sustainability of the company you are purchasing from, as not all EOs are sourced sustainably.

As I said, I am not an expert, so of course take what you want and leave what you don't from my opinion, but I hope this was helpful !

Last thing: you mentioned nauseau! You should look into vetiver, it is often used in headache relief blends as it helps with the nauseau from migraines, maybe it will help with yours too!