I'm lucky enough to live in an area that the evergreen yew grows profusely and is a common hedge found in yards. I harvest my own, clipping from the back part and then giving a nice soak in cool water before storing out in the cool outdoors until I'm ready to use it.
If you don't have this, you can substitute other common cut evergreens you can buy around Christmas time like flat cedar, cypress and juniper.
Whenever inserting greens, you can stabilize the piece by firmly holding the globe while you push the greens into place.
The goal is to choose different greens with color variances and different looks.
Doing this will add a lot of interest and beauty to a holiday design, where the greens play a huge part in the final look.
Here's a closeup of the yew I put in the end.
Even from the above you can easily pick out where I put in the yew.
This greenery is more lightweight than the heavier, thicker stuff like fir.