Does anyone have any tips on how to help make sure a baby field vole stays alive before I can release it if I can release it yet?

I found a baby field vole in the middle of a path in the woods that i thought was dead until I picked it up and it started moving a bit. It nuzzled into the gaps between my fingers for most of the journey back home and has been getting more vocal by clicking and (sort of) squeaking. It has perked up a bit but not enough for me to be happy it will survive.

Does anyone have any ideas or tips as to how to help make sure this creature stays alive before I can release it if I can release it yet?