Hey ab1215,
Someone else here recently asked something pretty similar here. That thread was more focused on protecting the feel of the mattress, but a lot of the same protector choices apply.
Between the options you mentioned, I’d personally lean wool-filled for your situation. Cotton protectors can feel nice and stretchy, but once there’s a lot of perspiration involved, cotton tends to absorb and hold moisture more like a sponge. Wool behaves differently, it wicks moisture away and disperses it better instead of trapping it right under you. That usually translates to sleeping less clammy and less “heat trapped” during the night, especially when there are two people generating body heat.
Wool also does a better job dealing with body oils over time. It’s naturally more temperature regulating and breathable than the waterproof/plastic-backed protectors a lot of people end up using, which can basically turn the bed into a sauna. You may want to consider a light wool filled comforter too. I know it sounds hot, you know, wool and more wool, but it is actually quite heat neutral. I use a wool filled protector under our sheets and a wool duvet above us and we do not sleep hot at all.
I actually went through something very similar with my son-in-law, who had a pretty serious sheet staining issue from perspiration/body oils. I ended up getting them DreamFit Long Staple cotton sheets along with a wool-filled protector, and according to my daughter the yellow staining issue basically stopped becoming a problem. More importantly, he also stopped waking up overheated. Before that they were using one of those cheap waterproof protectors and sleeping hot every night. Practically creating an 80’s sauna sleep suit.
Another option is linen. I use @BalooLiving linen pillow cases and they are just amazing to sleep on. After a couple of washes, they get soft and comfortable, almost calming against your head and neck, and sleep quite cool and dry.
If your main priority is maximum stretch and preserving every bit of the mattress feel, then something like Berkeley Ergonomics or CozyPure probably wins. But if your bigger concern is moisture management, heat, perspiration, and protecting the mattress long term, I think the wool-filled options like Woolroom Deluxe Washable or Shepherd’s Dream make more sense overall.
You’ll probably notice a very slight change in surface feel with wool compared to the stretchy cotton protectors, but usually not enough to outweigh the temperature and moisture benefits for heavier sweaters.
Hopefully this gives you a good start on solving your heat issue.
Maverick