Certainly fit blinds on the Velux windows, but on any window you can actually reach, outside shutters are more useful for keeping the sun out, and the temperature indoors reasonable.
Unfortunately, outdoor shutters and casement windows that open outwards are not on speaking terms with each other.
This means you either need casement windows that open in to your room, which will be well-nigh impossible to find in the UK, tthough the are standard fittings in Germany and the Netherlands, or you sill need to do as Spaniards do, and simply take your windows off their hinges at the start of the hot weather and put then on a gain come autumn.