Very comfortable memory foam Twin XL mattress topper with a cover layer:
https://www.ikea.com/us/en/p/tananger-mattress-topper-white-80466245/?utm_source=google&utm_medium=surfaces&utm_campaign=shopping_feed&utm_content=free_google_shopping_clicks_Beds_&_Mattresses&gad_source=1

Selling because switching to a bigger mattress. Pick up on campus. Please contact using Stanford email thank you!