In my experience fare basis doesn't matter, unless I somehow manage to book the correct fares each time. Which I doubt. No matter, here's the bottom line: once PN space opens up you can request an upgrade. If things work for you like they have for me then once you are booked and PN is available it will likely ask you if you want to upgrade through a link in your reservation in the spot where it typically says "Complimentary Upgrade Requested" or "Waitlisted." If there is no link for the upgrade and there is indeed PN space then call. If trying to use that link in the app there's a good chance it will fail. The website worked for me a few days ago the last time I tried: B fare domestic / O fare INTL. As a 1K I have never had a Y/B/M upgrade clear on its own, whether was a full fare Y domestic ticket or a B fare associated with a PP INTL leg. It always took effort on my part to call to get it done.

Keep searching your flights to see what fare buckets are available. Once PN opens up initiate the upgrade: call or use website if there is the link in your reservation. In practice the word "Instant" as a name of an upgrade type is a misnomer. Also realize that as a 1K you're competing against GS for that PN space. Depending on the route and the passenger mix you may never get a chance at the upgrade (highly likely).