If using wood I would suggest you make it out of laminated wood instead of a single board. It will resist movement a lot better, all wood moves.
If you want something other than generic pine or Tas Oak/Hardwood try giving someone like
http://mathewstimber.com.au/ a call and see what they recommend. Find out if they also have a milling service to help make the laminating work easier.
If you need any help shoot me a PM I might be able to help with the glue up etc...
JJZ