Lettuce and broccoli grow in similar conditions, and lettuces will benefit from the shade cast by broccoli in late spring. They'll also suppress weeds and improve the soil.
Onions and garlic are some of the best companion plants for pest issues, as they can reduce damage from most common brassica pesrs. Onions may even improve broccoli flavor.
Marigolds can repel or confuse pests like whiteflies, aphids, and caterpillars. Nasturtiums are great for pollinators and a useful trap crop for aphids!
for more companion planting ideas + what not to plant with broccoli