would " 's zondags rust ik" be a good alternative?
That would be "on Sunday I rest." Implying that it is just this Sunday and not every Sunday.
I don't believe that's right. If you want to refer to this Sunday exclusively, then you say "Op zondag". 's zondags refers to a repeated action taking place every Sunday.
Agree, it's definitely about each Sunday, so it has to be " 's zondags "