Just my opinion:
If you do wind up wearing a feather, make sure it looks absolutely nothing like an eagle feather. (i.e., it should probably be long, slender, striped, and lay back along the hat rather than stand tall.)

A hackle, as you have noted, is more often seen on a Glengarry. I think they're often seen as symbolic of military service. (For example, each of the Scottish battalions in the RRS has their own color hackle worn on their tam o' shanter and many other military and para-military organizations use a hackle in some of their headgear.) I haven't seen many hackles being worn in my part of the world.

I think a plant badge would be the way to go. If you have no clan affiliation, I think a dandelion would be, well, dandy!