I made the mistake of buying a pillow top mattress a few years ago and have been having back problems from sleeping on it. Adding this topper has made the bed way more comfortable and I am sleeping a lot better, I don’t wake up with severe back pain anymore. It fit under my bed bugstain mattress cover as well. My fitted sheets don’t fit as well anymore but that’s okay. I recommend firm over medium to anyone who’s a back sleeper with back issues. Great purchase!