Lock iPhone without pressing button

The phone can go to sleep on its own based on the configured time you would have for it.

The lock button is there for this type of purpose. It's been better compared to the earlier days and most people don't run into issues of it wearing out.

 

The button is meant to be pressed. It is what it is built for. Don’t be afraid to use your phone exactly as it’s intended.

 

My wife's iPhone 6 Plus physical button still functions fine as does my Samsung. Use it as designed.

 

You'll be fine.
It wont wear out, its a button designed to be pressed.
You will most likely upgrade devices within a few years anyway, you wont use the same phone forever.