When you replant in the spring and the sprouts start coming up, pinch off all but the largest sprout. When that single
spout is 12-18 inches tall, pinch off the center candle. This will cause the plant to be thicker, bushier, and have
thicker stems. You will have a 3-4 feet tall plant instead of
5-7 feet with thin stems.

some cultivars are more floppy than others, perhaps you need to get some with stronger stems.
Are all your plants wobbly, do they get full sun? And feeding too heavily has this effect.

Well, good luck next season, bye, Lin