I'd really appreciate some help as I've got very confused, though quite possibly am just being stupid...

I have a site being developed at mysite.co.uk/cms
(which is eventually destined for mysite.co.uk)
and I keep having issues with c5 writing when I try to insert a link to a page.
Partly I'm confused because I was used to working with site.php and
define('BASE_URL', 'http://www.mysite.co.uk');
define('DIR_REL', '/cms');
but this seems to have disappeared in 5.5

and now I have just found this:

5.5.2.1 Release Notes

Bug Fixes

Fixed double slash in front of index.php when inserting links in TinyMCE that would lead to pretty URLs not showing up in content blocks.


is this my problem?

Edit: upgrading to 5.5.2.1 does appear to have fixed it!
When upgrading older sites - can I get rid of define 'BASE_URL' / 'DIR_REL'?

and while I'm here, could someone possibly clarify for me what I'm now supposed to have in site.php (and in my .htaccess for pretty URLs) to get all my URLs back in sync and working in the /cms subdirectory?

Thanks very much