Doesn’t that make sex rather difficult?
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It is a little bit more difficult, especially when changing positions. You don’t get the same leverage or momentum when rolling about. And, if you’re giving off a lot of body heat, it makes it a little extra squishy.
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The best bed is mine. 
Lady Dopers should feel free to come and verify this.
I have a Select Comfort mattress (sleep number) and I love it. Actually, I’m on my second one - the old one is now in the guest bedroom.
I tried a Temperpedic and hated it. It was like a marble slab.