Hi...
You saying that Cadgwith, I sleep much better with a heavy duvet on top of me...I've never heard of a weighted blanket! I thought it was just me that needed the heaviness on top of me, it makes me feel cosy and safe especially when I have anxiety attacks. 
In fact in the summer when most people are sleeping with just a very light duvet or just a sheet even, over them, I hate it, obviously, if it's too hot, I don't sleep with a 13:5 tog over me, it'd kill me, 😂 but certainly I know exactly where your coming from...good luck with your purchase, hope it helps you...x