The separate base unit of a steam generator iron makes it somewhat bigger than traditional steam irons. However, most come with a hose which is long enough to allow you to place the unit on the floor so that it doesn’t take up extra space on your ironing board.
There are now some models of ironing boards which are designed especially for use with steam generator irons and have a built-in steam/condensation collection tray underneath the ironing table. These tend to be more expensive than standard ironing boards, but aren’t really necessary, as you can use your existing ironing board. However, if your current ironing board has a particularly small ironing area, you may want to look for a new, larger one, to complement your new steam generator iron.