• I adore these Quartz Crystal ornaments from VivaTerra! They look like beautiful icicles dripping from the tree, and promise to catch and reflect the light.
• This garland from Anthropologie is made of tiny pinecones dusted with snow (paint) and would look precious on a tree. For some reason the tiny pinecones make me think of tiny squirrels...I'm just gonna go with it!
• The best part of these Flora Grubb designed living succulent ornaments is that they will last the holiday season and can then be planted in your garden!
• Acorn caps were collected by Etsy seller House of Moss and then set with felted wool to create these adorable ornaments!
• toHOLD creates unique modern ornaments that are made of acrylic squares with an air plant affixed to the front! An interesting combination of living plant and modern design.
Images: As credited above.
100 DIY Ideas for the 3-Day Weekend
Danielle's Charming, Classic Walk-Up
Good Food to Share 
The Big Book of Small, Cool Spaces 
Apartment Therapy Presents 
The Eight-Step Home Cure 
White Enamel Flatwa...
How To Cook Fluffy, Tasty Quinoa
Perfect Summer Cocktail Recipe: Honey Bourbon Lemonade
I love being the frist to point out the contradiction between a plastic tree and natural ornaments! lol! Hey, whatever puts the merry in your Christmas - more power to you!
Here are some nice alternative acorn ornaments that I've been thinking of buying.
A reminder: if you want to actually SEE them, ornaments need to contrast with your tree. I got some lovely (non-natural) peacock ornaments last year in shades of blue and green -- they disappeared! This year they will grace a manzanita branch in the entryway, not the green (fake) tree, so at least i can see and enjoy them! (So the succulent above might vanish, too...)
I love the crystals, as well.
But I will also pipe in that adding NATURAL ornaments to a fake tree adds to the illusion that the tree isn't fake, which all of us who use fake trees for whatever reasons might appreciate!
Pomanders really "pop" against green tree needles (real or fake), smell great, and can biodegrade when it's time to toss them. Just make sure they're completely dried before hanging - citrus juice is sticky and you won't want it on a tree you'll be using for years.
Just fyi, some people think the allergic reactions might be to the cr*p that gets sprayed on the tree, not the tree itself. I have seen reports that if you can squirt it off outside, there are fewer reactions.
Of course, one sort of needs a yard for this. But maybe they would do it at the lot for you?
And then it might drip on the floor if you don't let it dry first.