2XU makes an awesome trisuit. I have the Super Elite and the Endurance Trisuit. Zoot is pretty good, too. Personally, the one pieces are a lot more comfortable, and you can slip in and out of a wetsuit a lot easier/faster so your transition times will be better.
Make sure it's tight. And I mean VERY tight, but not restricting your breathing. Getting the trisuit on should not be easy. Do you not have a store in your area that caters to triathletes? Without trying the suit on and having somebody else with you who knows how they should fit will make it difficult for you to get a really good fit. They do stretch in the water ...
And buy some body glide to put under your armpits and in between your thighs.
If you need a wetsuit, spend the extra money and get a 2XU. They are unbelievable. I have to wear a mens small because I'm too broad in the chest/shoulders to fit the womens. I suggest the C:1 or the V:1. Those are an absolute dream to swim in.