A couple of things I've tried with slugs Eliza is to take a fairly large plastic plant pot and cut the bottom out of it. Make sure you leave a a nice sharp edge where you have cut. The slugs won't go over that edge, they don't like it. You can sow your seeds and set the pot over them.
Another is to put saw dust around the area you have sown. The slugs don't like going over that either. You just have to watch it doesn't wash or blow away.
Slugs only eat the young plans. As the sunflowers mature the stalk becomes rough and spikey and they won't climb up it.