Opening Repertoire

I suppose you advocate for the closed structures of the french mainly, in that case and if you wnat to remain "closed" I'd recommend Stonewall or trying to approche closed structures of the Nimzo and Bogo-Indian, but these are black squared based. But what I think you should do is try more flexible structures, that way you'll be force to learn all kind of positions and improve really in chess understanding. For that kind I'd recommend 1 e4 e5 and 1 d4 d5 (slav, semi-slav) or Nimzo + Bogo.

Nimzo Indian is probably the most simple and effective defense against d4. I would really suggest it (although I don't play it)

Nimzovich Indian is by no means simple: it is complex. Besides often it does not happen as white tends to avoid 3 Nc3 and plays 3 Nf3 instead. White can also play g3 and enter the Catalan, which is also very complicated.
I still think the Dutch is more straightforward.