Growing to a height of , Simson established himself at senior level in the 1989 season. That year he was the winner at the AAA Indoor Championships with a throw of . He was also runner-up to Paul Edwards at the UK Athletics Championships and second to Simon Williams at the AAA Championships. He also made his senior international debut, competing at the 1989 European Athletics Indoor Championships where he came in eleventh place. He improved his personal best to in 1990.