Gonna try trex as new bed wood question

[bautino95]

Hi all. I've done some searches about the trex or composite decking bed wood replacements but have one question I didn't really see addressed in all the old post. The original wood is 3/4" thick right? I cant find composite decking with that thickness. Only a little thinner or thicker and I don't want to mill a whole board down to the right thickness. does it make a big difference if its say 5/8 or 9/16 thick compared to the 3/4 thickness where it sits on the ledge at the front of the bed and at the rear at the tail gate. Hope that makes sense. thanks