Petra and Mateo have been saving for the last 5 years and are finally buying their first home. They are nervous because their budget will be tight once they move in but they are confident that they will make it work. They would like your help on deciding the type of mortgage that they should take. They would like to pay the debt off as soon as possible and they believe that interest rates are likely to decrease in the next 18 months. They do not need access to extra capital. What type of mortgage would you recommend?