2 piece sweat suit for the junp suit, and maybe modify a sweater for the top, if it is for a quick Halloween costume. Otherwise you may have to make a jumo suit by hand.
I used a set of Cargo pants, a long sleve tshirt sleeves sew into a short sleeve tshirt, with a white button up cotton vest from walmart for the armor vest. Turned the vest backwars so the buttons were on the backside and covers by the back armor. The collar of the vest i turned up like a turtle neck and pinned it in the back at the top. worked out pretty good the waiste was covered by the belt so it didn't really show and it was easy to get my daughter in and out of.
here are some pics http://webpages.charter.net/gregseverson/ArmorSales/BobaFett.html