After months of deliberation, and some trial runs (using a large box to
put both keyboard and mouse on), I bought a kit of Jarvis adjustable-height
desk legs, and a Newlife foam mat.
Assembly of the kit was easy, using an old desk surface I had laying around.
The experiment has worked great so far: the mechanism is very silent, and
fast enough when changing height. It has four available memories for
different positions, altough the LED readout for the current height is
too bright and I (like many others, judging from online reviews) had to tape
it over with a bit of electrical tape.