Maybe you'd be interested in a smaller camera like the Sony RX 100ii? Seems like it might be perfect for high-quality off-the-cuff photos, and with a big sensor and an f1.8 lens it ought to do very well in low light.
I have the Mark IV, it's a great little camera that I use for mountain hikes. But it's not discreet or small enough to just pocket daily. Also doesn't do Instagram live videos, or allow me to upload stories at that moment. iPhone pretty much required.
Also! It's confirmed the new sensor in the XS is 32% larger than the X, which is SIGNIFICANT.
The XR is getting the same new sensor, so if you want to save a couple hundred bucks and can wait a month, it might be a thought. (That's my plan, less for absolute cost-saving reasons than I think I really want one of the colors that are only going to be available on that line.)
Decided this time I'm just taking the iPhone Upgrade Plan path, and treating the phone as a service. $55 a month interest free, and a new phone ever year + roughly $500 yearly trade in. Also comes unlocked, and without carrier contract.