You should find your swimwear before you go on vacation. Prices at resorts can be astronomical and you don' want to spend all of your time looking for swimwear that fits. Make sure you take your measurements before you start shopping ad use your measurements, not size numbers to find your best fit. Choose your tops and bottoms separately so that you can create a custom tailored suit.
Many one-piece suits will show more back and less tummy, others show a bit more cleavage or thigh. Show off your best assets and conceal the others. If you're into swimming, definitely get a one-piece. Find one that doesn't cut into the shoulders, has comfortable, and stretch fabric.