Don't upgrade your production server.

Then, there are two general ways of getting Perl on Solaris. Either you get all your tools from http://sunfreeware.com. Or you use the Solaris toolchain (SUN Forté C compiler). You can't mix them.

Once you've decided which way to go, build a test machine, and install a second Perl in parallel to the first Perl. Test that everything still works.

Then, consider either upgrading your production machine or promoting your test machine to production and then fixing the now defunct old machine.

I recommend /opt/perl as a directory to keep additional versions of Perl. And never touch the Perl that came with your system.