Soundproofing?

[kalipygian]

You could put in a layer of vermiculite a foot thick, and use a hammock.:biggrin1:

Just kidding, but that would work.

Besides the carpet suggestions that have already been made, a foam mattress or a futon would dampen sound transmission a bit.
There things that could be done if you owned the place, to do it well would require taking up the floor, or adding to the ceiling below, or both. A double layer of staggered joists and rafters, with the ceiling below attached to one set, and the floor above to the other, and fiberglass batting zig-zagging in the spaces.

 

[earllogjam]

Existing hardwood floors are hard to soundproof. It it is an old type floor not built on a plywood base you should try to seal any cracks or gaps between the boards and around the perimeter with wood chalk. A thick wall to wall rug for your sex chamber is a good suggestion already mentioned here along with a rubber matting underlayment product like Regupol which will dampen sound and impact vibrations. I think redoing the walls is overkill as is pulling up the boards to isolate your floor and inserting fiberglass insulation especially if you don't own the place.

Something that has no cost and will help a great deal is if you keep the windows tightly shut when you have the sex. It will keep your moans from any open windows below. Good Luck.