Though mas bands provide costume options such as tanikis and whole suits, a more flattering choice for a plus sized masquerader is the corset as pictured below, worn by Rachel Price in Island Events:
The other would be to customise your corset yourself. In this regard you can either purchase a corset that matches your costume, reuse the decorations from the regular top you ordered and even add extra beads and sequins. If you are not creatively inclined a seamstress can also do this for you. In fact, a very good seamstress can make a corset to fit as well.
I have seen the corset trend become more popular over the years, Destra Garcia wore one in 2006 when she played in Island People's PRIDE, Trini Revellers for 2007 had several sections with corsets and I even saw a few ladies in the Majorette section of TRIBE this year sporting decorated corsets.
So, just another idea on how to look fabulous for Carnival regardless of what size you are!