I'm no designer, but seeing as no one else has chimed in, I would go inside mount light blocking. Don't ask me about color or style, though.

Thank you so much for the suggestions. I am so glad I found this forum--this is exactly what I was looking for. Sometimes you need fresh eyes. I can see that this site could be a bit addictive! So I didn't think I liked shorter length curtains either, but I'm reconsidering that. Thanks for the helpful photo & input, roarah. I never would have thought about the difference between sill-length and a bit lower, but I see your point. I don't really want Roman shades, as I want to keep the blinds, and I'd like something to cover the sides of the blinds, but thank you for the suggestion. As for the panels to the floor, that was my first choice, but the radiator cover extends out so far that I'm not sure that will look right, even with holdbacks. I have printed out a couple of pics of the window above the radiator, and I'm going to sketch out your suggestions to see how they look. I'll let you know what I decide. Oh, and the bed: There is a floor vent between the bed & radiator cover, so we can't move the bed too much closer. Luckily the frame is on wheels, so it's easy to roll when making the bed. One more question: Normally I line draperies, but since I'm using burlap, I wonder if unlined might look more light-diffusing & charming. Thoughts? Thanks again!

Thanks @loobab! That bedding has turned out to be perfect in every way. It has become the inspiration for the whole house color palette. As often happens with decorating projects, I now have a new problem to solve. I have no place to put all those decorative pillows at night. There’s no other furniture in the room besides the bed and nightstands. Adding a bench at the foot of the bed seems silly with all that space on the sides to work with. A chair would be nice, but what else to put with it? I don’t need or want a dresser. And we don’t watch tv in that room, so a media console isn’t relevant. I fear just plopping a chair in one corner won’t be enough. Please help!

What is currently up there are just temporary/paper shades 😇 We had honeycomb shades there before which were very similar but my son “mistreated” them and they would not go up and down. I was thinking of replacing the shades. So I thought honeycomb (even though he broke those before), roller shades, Roman shades, or maybe even wooden blinds. He does not want curtains and he does not want a single shade all the way across (even though I tend to think a single shade would look nice). Thank you!!