Sorry I don't know much about Italian Cyprus but I think if you have mg seeds I'd try those first since they are inexpensive and bloom all summer once they get going!
The clematis is only a spring bloomer ( that variety ). It may take longer to cover as well . Good luck either way ! :)

Clematis montana will cover a small house. It will almost certainly smother your cypresses and kill off any remaining green parts. I would not grow it up any living thing, except possibly a very large, old and declining deciduous tree.

Thanks everyone for your feedback. I didn't know that the montana will kill the cypress, Anyway, I've started some MG seedlings at the base of the cypress:)