I'm not actually cold at night with my 4.5tog duvet BUT I want something heavier and cosier - is the only answer a down duvet? My son has a wool one and I don't like that at all. My current one is M&S, I think some sort of hollowfibre filling - it's soft but quite light, and I've stayed in some Airbnbs recently with lovely cosy heavy duvets but not been too hot. Can anyone advise/recommend please?