Answer: You didn't mention whether or not you've pinched back the stems of your sedums during the growing season. Pinching out the tips 2-3 times during the early and mid-summer months will produce dense and bushy plants which are able to hold the flowerheads upright as they develop in late summer. You can try pinching them back now, but the flower clusters they produce will be smaller than they would have been if you pinched back earlier in the season.
Bellflowers can lean or topple over if they've grown too fast (could be weather related or an overdose of nitrogen fertilizer). Whatever the cause, I'd stake them upright or put a peony cage over the plant and prop it up that way.
Best wishes with your garden!
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