[Renate]

Threre are so many Bluetooth remotes out there to choose.
Any of them can do what you want if you can map the buttons with a keylayout.
You'd need to be rooted so that you can write a keylayout file.
You could do the same thing using Accessibility, but that would affect all keyboards.

Two things to watch out for:
Selfie clickers often have too short a sleep timeout. 60 seconds is often too short for page turning.
Anything that is selfie related and is "iOS compatible" often send multiple key presses for some buttons. This can create problems.

The Bluetooth remote I built uses a commercial case. The part list by itself costs $25.