I usually stuff the cavity with onion, celery, and apple. And whatever fresh herbs I have on hand from my garden. The ones that go good with poultry include parsley, rosemary, thyme and sage. I use all of those because they are free, but if you have to buy herbs, I would just buy the sage. Buying all of those for mire poix is too expensive. It's mid-November in Wisconsin and my herbs in the garden still have not frozen. Normally I cut them all by now because we should have had a hard freeze a long time ago. I wash, spin dry, wrap in a paper towel and into ziplock bags in the crisper drawer in the fridge. The rosemary, thyme and sage stay good all the way into March! If you are smoking just the breast, you won't have a cavity to stuff, so you won't need the mire poix.
I'll be smoking a turkey for Thanksgiving this year, and using DM's poultry brine. I usually use my own brine recipe, but I'm looking forward to trying the orange juice in the brine. Bet that tastes good. I also like to add several slices of fresh ginger to my brine.