What type of shoulder rest should I use?

You can compare shoulder rests to eye glasses. You cannot really get a good recommendation for either unless you try it and see if it fits. On the whole we prefer shoulder rests, which don't touch the back and inhibit it from vibrating. Some shoulder rests touch it when pressed too hard and leave marks on the back. That translates into a costly retouch work. For example the Plastic "Kun" shoulder rests are known to bend too much when pressed and leave marks on the back. The more expensive "Kun Bravo" are made of wood and don't bend. In the long run they are cheaper, because you won't have to pay lots of money for retouch. Go to a violin shop and ask to try out many different shoulder rests before you make the decision. Some of them are adjustable in height. I prefer those. But the shape varies and your neck and body build will determine what works best for you. Good luck, Robert