A Z7II would be a good match for your current needs. If you can swing it, a Z8 is a much better, more versatile, camera.
Do you have the lenses you need in F-mount? Would you need to buy more lenses to do what you want to? Are any of your lenses screw-drive or are they all AF-S? If you have third-party lenses, are they new enough to be compatible with an FTZ adapter?
Do you shoot your portraits in a studio setting, or are they informal, decisive moment style? If the latter, the Z8 would be a great help as the customizable AF areas are much better than the, by now, dated AF in a Z7II or D850.