I’ve been using John Kinkennon’s idea for making a swell pedal controller for Arduino and it works great. It usually mounts to the floor of the organ and the existing hardware on the back of the pedal, so that is one solution. I can give you more details and even the code if you’re interested.
That being said, many people are fond of the so called “rollschweller,” and they are very popular in Germany, so you may very well find you like it.