After some experimentation with various styles of shoulder rests I eventually found an adjustable shoulder rest from Bonmuscia. It is easy to adjust and once you decide upon the appropriate angle you won’t worry about it slipping off the violin nor off your shoulder. I recommend removing the shoulder rest before putting the violin in the case; if you must leave it attached to the violin, use some coloured tape or paint (nail polish?) to mark the correct position of the screws connected to the feet. Regardless of the shoulder rest it is essential to remember not to apply too much pressure with your chin/jaw against the chin rest.