This is the perfect topper for a firm mattress. It feels so luxurious but still allows for good back support.  I fluffed it in the dryer as suggested and it did make a difference in how it opened up the fibers. It feels like you are sleeping on a pillow. It has large elastic straps that will work with a 12” mattress. No problem putting my sheets over the topper. I can’t wait to sleep in it tonight. Makes the bed so welcoming.