If the spring shop doesn't have an oven (furnace) to heat he springs before re-arching it won't help you. If they just use a press to re-arch (cold springs) they will start to sag again very quickly.
Another option is to add another main leaf to the spring pack. Get one that's close to the right length from a salvage yard and cut the front/rear eyelets off. Install it right below the main leaf. That should get you back up to stock height or a little above.
