Raul,
NS already comes with nsssl built in.
Do you have SSL certificates already?
If so, you just need to edit your oacs config file for NS. On ubuntu installation the filename is usually as in "oacs-config.tcl"
Uncomment line 549
#if {[info exists address_v4]} ...
and modify paths to your certs, at line 424
ns_param certificate $serverroot/etc/
lines may vary depending on oacs-config.tcl
Be aware of .pem format file. IT must be fullchain plus private key.
Best wishes