Bernina has its own ruler foot and ruler set. I have had fun with mine and haven't purchased any others yet. The one ruler I want is a nice big arch ruler for curved crosshatching. Some rulers have a strip on the bottom to help them from slipping and that might be helpful. I bought the little gripper circles but they don't work as well as the little squares of shelf lining underneath that Gina Perkes recommends. Her video series is on The Quilt Show.
The Westalee company is really good if you need a generic foot and rulers for your machine.