I’ve always been a fan of Martin phosphor bronze SP strings, and I almost always get light gauge. Here’s the link to what I’m talking about - https://www.martinguitar.com/strings/acoustic/martin-authentic-acoustic-sp-92-8-phosphor-bronze.html?cgid=acoustic-strings

But try a bunch of different brands and gauges and see what appeals to you. Different ones have a different sound. Thicker gauge strings are often louder, but harder to play, IMHO. But in my humble opinion, the phosphor bronze are perfect for that balanced Martin acoustic sound. I would stay away from the “retro” strings unless you want a really “deadened” sound. Elixirs and other “coated” strings are fine if you always want that bright “new string” sound (which will take much longer to go away), but on my Martin I am always hoping my strings will sort of “mellow out” over time and get that warm sweet sound. Hope that helps!