hey, i found this, and you can use less of it and on many other things, not just mac and cheese. i hope it helps.. i want to make things better for you.
table salt as you know is huge,, so, also consider lemon pepper.. some brands are even less sodium than others (but you have to look on line, as its not always on the bottle for some reason)
and dont forget, if you are allowed some types of salt subst (you said some you cant but maybe some you can).. get "also salt" its wayyyyyyyyyyy tastier than the usual salt free salt. and has NO sodium. i think celery salt is also low.. but would have to verify that.