If Bush wants a safe and easy pick then he'd nominate a Senator.
Rick Santorum or John Cornyn would be excellent choices. You Dirty Rats suggested Jeff Sessions. Any Senator would practically guarantee unanimous consent. You can't get any more conservative or qualified than those I listed.
What is needed is more imagination and less "woe is me" excuses.
Which of these guys is in the mold of Scalia and Thomas? Actually, I've always liked Sessions because he is one of the smartest guys in the Senate.