"Kristen is quite dark so she wants a ceremony performed by a New Orleans voodoo priestess," a source said.
"They've both had the crazy highs and lows you get when you're intensely in love and thousands of miles apart, plus they've been coping with the immense pressure of conducting a relationship in the public eye."
"But they've now agreed they are serious and want to make a love pledge to show it."
The couple wants to get each other special love tokens and make matching tattoos.
"Instead, Kristen and Robert want to buy each other tokens of devotion," the source added.
"They want to keep speculation to a minimum, so won't get rings, but each is going to choose a present that reminds them of just how much they love each other."
"And they're going to both get matching tattoos on their hips. They want tiny anchors to symbolize that they ground each other and keep each other calm when things get stormy."