Bundy,
Who do you fly with? Just curious.
We also sit in the aft galley on some of our aircraft. With our airline, we must have all finger locks locked and everything stowed away in the galley before take off and landing. This is one of our checks.
And as for the harness, well that is our crew seat. It has a full harness. But in the situation where a decompression would take place, we are taught to take the nearest seat possible, which may be a pax seat if this was to happen whilst we were moving about the cabin. If there are no seats available it's best to wedge yourself in between the isle or between 2 pax seats. Provided the backside fits of coarse!
Then its time to administer oxygen to yourself and the pax.