Louisiana

A sign of strength for Romney would be winning Louisiana. If he can win that state, he can soon win enough delegates for the nomination. This will allow him to win Texas.
If he does not win, then he needs to consider on getting a V.P. who is from the south and will do well in debates. Newt will do well in the south but won't be enough to help him. Santorum showed he can win in the south so he could work, but would he be good and debating V.P. Biden? He would need to work a lot to prepare for the debate.

So, assuming Romney get the nomination, here are some options
Rick Santorum
Bobby Jindal
Phil Bryant
Haley Barbour
Robert J. Bentley
Rick Scott
Jeb Bush (Could help get Florida, and attacks about Bush would back fire)
Sam Brownback
Nikki Haley (she is young, would be compared to Sarah Palin and would need to do a lot of prep work, She has to study hard to do ok against Biden.)