Catrin, do you cycle with mostly the forefoot on the pedal? Have you tried lowering your saddle 1-2 mm so that you can pedal with more of your arch centered over the pedal? Your knees may or may not like that but it's worth experimenting if it will help alleviate the pressure.

One of the perks about platform pedals is that you can wear all kinds of shoes. Just hop on an go!