Exactly. You have to use relative URL. The server and port will be automatically resolved from existing session.
And in the hyperlink, instead of the integer ID, use CUID and while migrating, do it by ID so that CUID remains same. If that is not feasible, you can use sDocName and sPath combination in link (for XI3.1) which to be kept same across different environments.
If someday you upgrade to BO 4.x, you have to use Promotion Management which will always keep the CUID same after migration. Also, in recent versions, it is recommended to use CUID in opendocument links.