I think you need to research the contact process.
AFAIK, elemental sulfur is oxidized stepwise to give
The sulfur trioxide could be directly treated with water to give
One thing the reaction has got going for it, is that both oxidations are exothermic. Sulfur trioxide may be directly converted to sulfuric acid:
But this opens another can of worms. Usually sulfuric acid is reacted directly with sulfur trioxide to give oleum,