Who is your host?
Most hosts will offer a way to choose the php version being used on your site, for example, with 1 and 1 there is an option in the control panel:
http://help.1and1.com/hosting-c37630/linux-c85098/php-c37728/change-the-default-version-of-php-in-the-control-panel-a792330.html
By choosing an earlier PHP version, you would be able to continue using the MySQL library.
We are currently working on eCart 6, that project will probably take a couple more months to finish, once eCart 6 is finished, we will be working on data Bridge, including the update to using MySQLi.