Okay, so what your are really looking for is a pasta sauce that will work with fish or chicken, right? With fish, I don't do heavy sauces, like I would with chicken. Two entirely different things, to me.
Béchamel, or roux, can be made in advance, and made into a number of sauces later. I have never frozen it, but I'm pretty sure it would work.
I think it is a matter of finding that balance between made in advance and made at the moment that you should look for. If you knock out the time-consuming and difficult stuff in advance, and add the easy stuff when you go to cook a meal, you will get the best of fast and fresh.
Roux is time consuming. If you can make it some day when you don't have much to do, and keep it for finishing dishes later, that seems like a great solution.
Experiment, and share with us what you learn. That's what this forum is all about, IMO.
CD