I have a double pink hibiscus that used to flop.i didn't make a hedge with mine so it is a freestanding plant, but after it flopped for a few years I chopped it back hard in the late spring and it sent out vigorous straight shoots and hasn't flopped since.
I think the key to growing them so they won't be floppy and messy is to prune them while they are growing. It doesn't effect the blooms because they bloom on new wood anyways
