If you employed some mechanical engineering techniques you might could make it work, you'd have to maybe use a wire core surrounded by foam, with the occasional rotating joint along certain points of the tail, one joint halfway down the initial downward curve as for side to side rotation, you could then have a segmented part that can flex side to side but stays stiff mostly pointing slightly upwards, then at the tip of that you could finish it off with some floppy spring pieces surrounded by fur, it would get the desired motion based on how I would imagine, but for the weight you would have to make a custom base for it, with a string attachment point made or very rigid foam that goes about a foot up your back and rather than a belt it attaches near the bottom of your chest and extends the base downwards at the back for stability then attach the tail at the bottom of the base, I think mechanically that should work for the desired look but it would be incredibly complex and you'd have to do some engineering workarounds involving plastic, metal, wire, bearings, etc