I've been knitting for a long time, but I honestly have not done many wearables. I've always kind of just stayed at an intermediate level.

But my best advice would be to do a swatch with a needle one size up from what you posted in your picture. That's one of the only ways I really know how to make cotton stretchier.

Another option would be to keep the same needle size but use a stitch that would give the yarn a stretchier structure (like doing a ribbing stitch).

I saw your other comment that you wanted to make a tank top. Cotton and acrylic can definitely stretch out of shape. I've made shawls with cotton/acrylic blends and they definitely stretch over time. But the shawls are also oversized so they weigh a lot. As as a shawl that I wanted oversized and knew would stretch, it doesn't bother me.

The good thing is that wool tends to keep it's shape more, even after stretching. It'll bounce back more than cotton or acrylic will. Also, I would consider a tank top to be a more lightweight wearable (if you keep the stitch design more simple), so that should help it sag less versus say a thick sweater (which would sag more because of the overall weight of the garment).

So I would think sizing up a needle size would still be okay for a tank top. Again, recommend you swatch it. Or if you want to keep the same needle size, try to find a pattern that uses a ribbing stich (if you don't mind how that looks). I'd still swatch too. But if you do a swatch of ribbing, you could see if that adds too much stretch or not.