I've just got some made to measure black out blinds, which I measured myself.
The handyman has just screwed them into the brackets. They fit, its a miracle (never measured blinds before) but not quite the black out I was hoping for.
They go inside the recess and the bracket they are fitted to makes them come forward about half an inch, so there is a gap and the light comes in at the sides.
If they were more flat against the frame it would be better.
Currently I've found some long pieces of cardboard to put on them at night.
Are there better brackets? Or something else I could do? Or I could move them to another room and go for blinds that go outside the recess.