Hi cviz,
The same tradeoffs would apply for a memory foam mattress that they would for any other type of mattress (see post #89 here).
For most people the thin “membrane” type of protector would be a good tradeoff for those who want something waterproof but has little effect on the feel of the mattress and don’t mind that it may increase sleeping temperature for some people because it is less breathable. For those where a water resistant (vs waterproof) protector is OK then a wool protector can help with sleeping temperature but may have more effect on the response of the memory foam. For those who don’t need waterproof or water resistant and only need something that can absorb moisture and body oils and small spills and is highly breathable and feels like a stretchy sheet with little effect on the mattress then a stretch cotton protector would make a good choice.
Phoenix