Warm curtains - suggestions?

[partyskirt]

It's getting colder and our toddler's room (with it's beautiful but crap sash window) is freezing. Does anyone have any recommendations for really good thick curtains? I am at a loss. Also they will need to be taken up as radiator is under window. Thanks!

Dunelm do some really thick blackout thermal curtain liners. I've got them in my very cold room and they are good. You just hook them onto the back of the existing curtains.

Perhaps a thermally lined roman blind to sill length and fitted so it goes beyond the window width would be better?

I had a room like that as a child and my dad fitted a giant piece of plastic with magnetic strips round the edges to stop the draughts. It's probably an actual product these days? Is that an option?

I lined DD's curtains with fleece (unwanted slankets) and her room is noticeably warmer