Hi tsume,
I don’t have any specific recommendations but there is more about the pros and cons of the different types of mattress protectors in post #89 here. One of the thinner membrane type of protector are popular choices because they are waterproof (or at least “mostly” waterproof), are relatively inexpensive, and have little effect on the feel of a mattress although they are also less breathable than other types of protectors so they can also sleep warmer for some people.
Phoenix