BRITNEY'S PLAN B FOR MOTHERHOOD

Pop tart & fiancé eye surrogate - just in case!

- 

UNCAGED songbird Britney Spears and fiancé Sam Asghari have baby fever, and the couple is quietly searching for a surrogate to ensure their dreams come true, sources spilled.

"They see surrogacy as a win-win, since they want more than one child and will likely go ahead — even if she does conceive, which has been the priority for several months now," snitched an insider.

As National ENQUIRER readers know, in November the "Toxic" chart-topper, 40, was finally freed from a constrictive 13-year conservatorship that forced her to live under her father Jamie's thumb.