Non-priority usually takes a solid 12 weeks, so I think you are well within normal timelines. Why do you think your case won't be straightforward?
My boyfriend and I lived together in the US until the end of 2016, when we left our jobs and gave up our apartment to travel for the year. We continued to receive joint mail to my parents' address (shared bank account statements), but we didn't actually live there. We provided all of our travel documentation (tickets, bookings, travel visas, etc), social media posts, photos, and text conversations, giving roughly biweekly evidence that we were together the whole time. (We literally spent every day of 2017 together, aside from 1 week, until I returned to the US to submit my visa application.)
Our immigration solicitor in Belfast tells us he thought we'd pulled together strong evidence and wasn't worried about the relationship/cohabitation proof. Still I'd heard from another solicitor that he's seen applications rejected because travel together didn't count as cohabitation. So, since I have nothing to do but wait and worry, I've probably thought through every detail in our application that could possibly lead to a rejection, and that section is a big point of anxiety for me.
Basically, if the Home Office is going to apply the spirit of the cohabitation rule to us (2 years living together), we meet it, no question. But if they are looking for a reason to reject it, they can probably throw the book at us with the 9 months of travel.