What version of Solaris are you running that is preventing you from installing the 12c client? What is the value of the NLS_LANG environment variable?
Sunfreeware is some sort of subscription service now IIRC, https://www.opencsw.org is an alternative. As someone who spends most of their day job on Solaris, with Oracle 12c, make life easy on yourself. Perl 5.5 is old and not maintained/supported. Build your own perl, install it to something like /app/applicationNameHere. Install DBI and DBD::Oracle the way you would any other perl module.