Argh, this is hard! I'm thinking more and more that using 100% alpaca was the biggest problem with my Mariah - it doesn't have the spring and strength of wool, and the whole thing is just too drapey and floppy. And I can't bear the thought of starting another nice top and having the floppy fibre not work again.
I've spent far too long on Ravelry, and using their Pattern Search facility, have come up with only a few cardigans that are on gauge (20-24 sts : 4") and in 8ply / DK, with not floppy sleeves, and in nearly pure alpaca. I think IVY is about the only option.