We had our blinds from Hillarys.
They come to the house ,show you what they have got and they measure and come back with them and fit them.
I would never buy Venetian,I have one in the caravan and it is a dirt trap.
Not sure what mine are called,maybe Roman,silky material so I give em a quick flick with the duster when I can be bothered.
They cost a fortune but I did choose from their most expensive range but I thought what the heck,you have to look at them a lot so they are worth it.