This. Or a mattress of some type on the floor, or really any other way to not be in the same bed. You don't need to buy a new bed, but you do need to not sleep in the same one.
I was told we do not need to keep all harchakos on Tisha B'Av, but yes on YK.
Not all harchakos, but sheina b'mita achas is one of them.
Some are lenient and allow 2 beds touching on TB (not YK) but I've not come across a shitta that allows one single bed that night.
