You can buy rods that have a return where it connects to the wall. That was the curtains sit snug to the side wall and blocks more light. Here is one I’ve used.

Blackout curtains are great, but you need to look at all the edges, as that is where light will leak out. In my experience that means:
A pelmet on the top.
Either one curtain or make sure they overlap where they meet in the middle.
The curtains need to extend well beyond he window at each side. The rail that Sharon has posted looks a good idea too.
Floor length sounds like a good idea, as long as you are not covering a radiator. Most radiators are situated directly below the window, so you end up blocking the heat. We have curtains that fall just below the window and tuck them between the radiator and wall. Aesthetically not ideal, but if you're asleep, who cares? Better than waking up to a cold room.
A more expensive option is metal roller blinds fitted into the window frame.

recordaras - did you order directly from the website and install yourself? Are yours motorized?

Here are the 2 windows I am interested in adding blackout curtains to: (see picture below)

I definitely would get a wrap around curtain rod - thank you for that idea. The one I'm interested in has 2 different sizes: 28-48'' rod or 48-88'' rod. Which size rod would I need?

Both windows are fairly close to the wall (only 15.5'' between the wall and start of the window trim). Is this enough space to have the blackout curtains? How much space on each side of the window do I need for the curtain? for the rod?

No radiators - so they can go all the way down to the floor. I should choose my blackout curtain, see what lengths they offer and then decide on the height of the curtain rod so the curtain is just barely touching the floor?

I ordered from BlindsChalet - measured myself, installed myself (it’s literally 2-3 brackets with 2 screws each! Super easy. Plus the stick on side tracks). We have regular Bali blackout cellulars in our bedroom and the difference is huge.

And ours aren’t motorized - our windows are small but high up so we did the cord loop.

Can anyone suggest a good color scheme for blackout curtains in this bedroom? Thanks!

Should I do white blackout curtains to match the trim/ceiling?