It you can afford it, use a cool circular elevator. Would add great value to your home if you one day sell.

Spiral staircases are illegal in most place now unless you have another means of escape from the same room that is you can have a spiral going to bedrooms but you also have to have an exterior set of stairs for fire escape thats why you don't see them so much anymore.The one in the pic is interesting don't know if it would pass where you live. I think the only other choice would be to make it as open as possible so visually takes up less space. The glass one is what I am thinking

The vacuum elevator is a great idea.