Thanks for the info on brushes, and everyone's input in this.
I've been experimenting and I've found the following to work best at suppressing the halo effect I was seeing. As I stated in my OP, I'm a newbie so there may be issues with this methodology but for what it's worth I did the following.
1) Make selection of subject
2) Refine selection
3) Create a layer copy of the selection
4) Invert original selection to select background
5) Create a layer copy of the background selection
6) Place background selection layer below the subject selection layer
7) Apply Gaussian blur to the background selection layer
Following Carl123's steps didn't seem to have an effect on the halos on my test image, but this might have been due to me not communicating what halos I meant effectively.