Thank you for your enquiry.
You only need 5 years evidence to obtain PR. If you have evidence extending to 8 years in total, you should be eligible to apply for naturalisation without having to wait 12 months.
You have misunderstood the change in the rule. You must first apply for PR in order to proceed with a naturalisation application. If you already have 8 years continuously residence as a qualified person, you would be eligible to apply for naturalisation once you have been granted PR. You will only have to wait 12 months if you only have 5 years continuous residence.