It is possible to have the complete or a part of the mortgage based on interest only.
In these mortgages there is now back paiment to the bank and there is only a interest due every month.
The hight of te Interst only part is depending of the bank of your choice. Some banks allow 100% of the execution value others won't go higher than 75% of te execution value.
The saving to pay back the mortage becomes more a private matter as the mortgage bank does not demands it to with them. The philosophy behind the product is that the mortgage will be paid back as soon as the house is sold.