I have used Pellon batting that is 60"
http://www.joann.com/pellon-siliconi...=false&start=1
It is very consistent and actually quilts up pretty nicely.
Fabric Hotel has some wider cottons. I have ordered from them and have been happy:
http://www.fabrichotel.com/55-56-nov...8cadad3444a7f5
If you can deal with a blend, you can look for broadcloth for backing.
https://www.fabric.com/find?collecti...rchText=cotton