Well, it's your call on what to keep but I've found that Susana Monaco runs tts or slightly small. I have about 4 pieces and they're all quite snug compared to other brands in the same size. You'd have to post measurements for me to estimate on sizing, though, a number size is too flexible these days!
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"Don't be cool. Cool is conservative fear dressed in black. Don't limit yourself in this way." - Bruce Mau
i'm your size and have a couple of pairs of juicy pants. you should go with the 31, which will probably be big, but won't swim on you. the 32s will definitely be too big.