Mortgage interest rates remain at historically very low levels, but lenders continue to tinker with product design to boost flagging originations. The latest innovation is a different breed of ARM that offers borrowers multiple payment options to achieve maximum loan flexibility. Countrywide Financial’s program, called the PayOption ARM, offers an introductory rate of 1.00 percent that lasts for the first year. After the first month, borrowers can choose to keep the minimum monthly payment option,…