Being a botanist, I have long used oils, mostly in my bathtub. Most recently, a genetic consultant who I really respect, Sterling Hill, recommended BERGAMOT oil for me as the National Institute of Health actually recommends it for the reduction of the excitatory neurotransmitter, glutamate, which causes anxiety which I have had tons of over the years. If you search you will find several NIH papers on Bergamot's wonderful properties. Here is one: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4345801/
I was just putting it in my tub with my magnesium Epsom salts and thought that was best. But for this last year, I have had severe shoulder pain and just yesterday was really getting a cold. A coach (Kim Saeed) recommended aromatherapy for self-care and yesterday my tiny little ten dollar diffuser arrived as well as FRANKINCENSE oil which I ordered as I had heard it was the Queen of Oils and indeed if you read up on its properties, you will be amazed. Most important, it is anti-inflammatory and I have lots of inflammation; many of us do and many believe it is the root of many, many illnesses. ( BTW I would say Dr. Josh Axe offers some of the best education on aromatherapy.) Here is a link to a great deal of information. Oils have medical uses and especially help with moods via neurotransmitters I learned. https://draxe.com/essential-oils-guide/l
So here is my own little starter kit. I choose by price and by recommendations of other buyers. I now use Frankincense, (my pain and my cold are much better), bergamot (reduces my anxiety) and lavender I bought locally for some soothing. BTW the diffuser I choose was only ten dollars! Next, I am looking into HYDROSOLS which are oils suspended in liquid for spraying. Do read up on them all before you use them. When I rub them on, I add them to coconut oil as they are not recommended to be directly applied. Some can be used internally but do study up.Here is a link to old beloved post on the sensing of wine as a form of qualitative reasearh. I especaiily dedicate it to fine wine maker,Gary Pisonii of Pisoni Vineyards.