I'm sure it can only help to make use of curtains or doors as the cheaper option. What I don't like though, is the old story of treating the symptoms rather than the cause.
The Count is dead right .......... I've detailed on here several times how to go about it.
Also ............ some time ago I outlined to someone how to go about Nono's suggestion. I prefer it for several reasons .......... no internal disruption, if it is masonry built, then external insulation would make the existing walls into a heatstore, also, it would be a great way of losing the .......... ahem ....... "brick effect" lol.
Easily within the scope of a confident DIYer, even if you had someone in to do the rendering.............. or DIY with weatherboard/tilehanging, or whatever.
It would put good value on the house too ........ easily pay for itself.
Don't be so tight Boolders .............. invest! ;o)