There's sweep 2 wake and double tap 2 wake function.

But you'll have to install a custom kernel.

And it drains your battery too as the digitizer is always active.

Double Tap to wake,
Swipe to wake,
Gravity screen

yes, volume rocker to wake up the screen.
without physical button, have more choice:
1. double tap to wake (aka knock on).
2. swipe from left to right the screen to wake up.
3. those using cover flip casing, can try smart cover app, which is using the ALS to detect the flip open or close.
4. buy flip cover with magnet feature