The topper comes with a washable stretch-over cover. It doesn't have any straps to attach to the mattress but that's not a problem - it stays put by itself. 
As for comfort, I love it. I'm sleeping much better. I'm so pleased with it that I bought another for our caravan!
There was a delay in receiving it caused by the courier. Wayfair customer service was absolutely brilliant, chasing up the courier & ringing me back after delivery to make sure everything was OK. I have 100% confidence in shopping with Wayfair again.