I didn't read through the thread, so I apologize if this is repetitive.
I freaking LOVEEE frankincense. I tried lavender, but it gives me headaches. I like eucalyptus a lot for anything except bed time, and for that I stick with frankincense. A got a diffuser for super cheap at a store that was having after Christmas sales....it fall themed, I guess? Still diffuses the air just fine....
I get my essential oils at the grocery store. That way I can look (and smell) in private, as opposed to a smaller shop or boutique. They have testers you can sample with. They carry an "organics" brand, but that's more expensive. The regular brand they have is "100% pure" which is what I've read you're supposed to look for. I have also read that citrus oils can wear down diffusers, so keep that in mind, whether that means cleaning it more regularly or whatever. I clean mine every two days, depending on how often I've been using it.
Yay! Good luck!