This past fall I planted spinach and carrots with my mine. You do know that in the South brussels are a fall crop only?

Yes, as Deborah says, don't plant in FL until summer heat is done. Same here in Socal.

I tend to believe companion planting advice tends to be more anecdote than science, but overall I believe in polycultures over monocultures.

They say alliums are helpful for brassicas. I tend to plant green onions (allium fistulosum) as a cut & come again crop along with other things. They do well as a cool-season crop.

Lettuces get along with lots of crops, and as they do well in partly shady conditions and cooler weather, they might do well in the understory with the brussel sprouts.

In terms of companion planting, I like to think along the lines of niches both in space and in time.

So, in terms of space we can look at tall plants vs, short plants, shallow roots vs. deep roots, etc.

Opportunities in time would be something like sowing very short season crops (such as a baby greens mix) alongside a long-season crop, such as brusell sprouts (120 days). The greens mix will grow quickly and you can start harvesting after a few weeks, gradually thinning the greens as the brussel sprouts need more space.