I have found what I believe to be some suitable plain bearings, however the website targets industrials, so I sent a request for an estimate (and some advice, too), but have not heard from them yet. A good news is that all the bearings are fully open on the inside, just like a cylinder, so we can easily set our angle measurement, such as the EE-SX1131, an inexpensive optical sensor. This is a joyful news, for setting the sensor up was quite complicated, especially finding a way to protect it from water and dust.
I looked into some springs to provide the necessary torque to stabilize the foot-platform when it pivots, and have found a design that allows us to easily set them up. I will upload some sketches in a future edit.