For what it's worth I bought a new drysuit last year. I looked at the Boost also, but went with the hybrid because most of my early season skiing is slalom also. I had a baggy style and the hybrid felt like less drag in the water. No problem staying warm with the hybrid. I believe I bought a L size. I actually went to the dealer and tried them on before buying the suit.
So I guess the real message from me here is to go to the dealer and try them on before deciding what size/style you should get. Fit of a suit is a persoanal preference, not an on-line survey. You don't want to make a $400+ mistake.