usil once bubbled...
Ah yes I have a back plate now but the damn thing is just way to uncomfortable when you are diving without a wet suit or in just a thin microprene.
I would wear a 2 or 3mm shirt so I could keep the bp. Only other option I can think of is one of the softpack "tropic" BC's. I think your size would be a problem there, as well as diving with a softpack sucks, IMO anyway.
I think the 18 lb and alum bp sound pretty optimal, especially at that price!
Phil