Buying a new iPhone every year is too expensive and not worth it. Apple doesn’t make essential changes to iPhones once a year, it does so once every three years now. Before it was once every two years.
In the image below you can see the most recent cycle of the iPhone design refresh for the flagship models. From left to right: iPhone X, iPhone XS, and iPhone 11 Pro.
As you can see there’s not much different about iPhone X and XS, not only appearance-wise but also functionality- and hardware-wise too. The only essential change was made to the most recent iPhone 11 Pro. Appearance-wise only the back design was altered, otherwise, from the front, the phone looks exactly like the previous two models.
It’s expected that Apple will make major updates to this year’s iPhone. With a brand new design and new features.
So instead of upgrading your iPhone once every year, you should upgrade once every 2-3 years. That way you’ll get significant upgrades over your existing iPhone model and it will be right before the battery on your iPhone becomes useless.