A lot of the soul of the upright bass is in the G string, and no other G string has as much soul as this one. It's expensive, but your bass is worth it!
I would also recommend getting the Oliv D string, but then I think the A and E strings are better off with something else, because the lower Oliv strings are too muddy, and anything else is going to be cheaper as well. My recommendation would be Pirastro Evah Pirazzi Light, or Medium if you like to detune your bass two steps like I do!