My solution above assumes there is already a cable with only a WB/G running from the single pole switch that’s going away to the light fixture. Generally the harder run to make with a finished house especially a two-story house is one in the ceiling below a finished floor. So I suggested using those wires that are in place already.
That then leaves running a cable between the old switch location and the new location on the second floor. Walls are easier to fix IMO. That cable needs to have the traveler wires WBR/G. that then needs a power supply cable to the upstairs WB/G. There may or may not be power close to that new switch location, but my thought was that needing to fish one new cable between the switches you might as well fish power along with the travelers killing two birds.