A 72-year-old man with known COPD presents with an infective exacerbation. On arrival his oxygen saturation is 85% on room air, respiratory rate 26/min and he is using accessory muscles but is alert and able to speak in short phrases. Arterial blood gases show pH 7.34, PaCO₂ 7.0 kPa and PaO₂ 6.5 kPa. According to Australian COPD guidance, what oxygen saturation target should you aim for with controlled oxygen therapy?