TotalBlack Roller Blind

A solid, straightforward roller blind with genuinely thick blackout fabric — you can hold it up to a lamp and barely see light through it. The catch is the same as almost every roller blind: without side channels, you'll still get a thin strip of light down each edge unless your window recess is a tight fit. Combine it with a cheap set of light-blocking strips (widely available separately) and you'll get close to the frame-fit experience for less money.