Plain jersey will be fine. If you happen to do well, you'll look all the more impressive.

Only rules about what to wear are 1) no sleeveless jerseys, 2) no replica jerseys of champion jerseys (i.e. you can't wear the rainbow colors of the world champion, unless you're the world champion), 3) you can't wear a jersey of a team of whichyou're not a member, and 4) you can't wear a jersey with advertising other than your sponsors.

1, and 2 will actually be enforced by almost all Officials. 2 and 3 not so much, but you don't want to have to worry about it, so a plain jersey is the best idea.