If you haven't tried any TENS or other types of stims ( like IFC stim) before, I suggest finding a physical therapy place that has a few kinds available, and ask them to see which might be best for you and then test it out before buying anything online.

Some can be used on battery power for mobility and some can also be plugged in to an outlet if mobility is not needed so much.. so you might check for ones that can be powered both ways and flexible placements.