We bought the 4" inch from
Walmart for my daughter. It is on a twin bed and she loves it. We purchased it about 4 weeks ago so I can't comment on long-term wear but it seems to be of great quality. We also shopped at Costco but the ones they sell (althought very nice), don't come in a twin size. The one at Walmart was something like $88 if I recall correctly and it has proved to be a great buy for us. Good luck!