You can determine chlorine + ozone with DPD/iodide and then determine ozone without chlorine interference using either DPD/iodide/glycine or indigo trisulfonate. I think the latter is most precise.
For Chlorine the most simple method is: APHA, 2012. Standard Methods for the Examination of Water and Wastewater, 22th Edition. 4500-Cl G, DPD Colorimetric method. See also atached.
For ozon see APHA, 2012. Standard Methods for the Examination of Water and Wastewater, 22th Edition. 4500-O3 B.