The HVAC tech is right about the loss of efficiency.
The "proper" way to cool just the upstairs is to install a zoning system on your HVAC, or install a second HVAC system and have each system supply one floor. That's expensive, though. Another option is to set your thermostat to run the fan all the time during the day, so it recirculates air throughout the house.
You might also consider installing a radiant barrier in the attic, as well as more insulation.