Combining two pieces of different weights?

I’m knitting my brother a patterned hat for Christmas out of Patton’s DK superwash, which is not the softest wool in the world, but it was the only DK natural yarn available at my LYS (I live in Hawaii; we have few LYS and most of those stock cotton or acrylic, which I’ve read would not be the best materials for cold weather items). I’d like to make a second, smaller hat out of softer material (probably acrylic) and attach it to the inside as a liner both to reduce any possible skin irritation and to hide the strands from the pattern I’m working, but the problem is I only have worsted or sport available. Would it be possible to make a smaller hat and sew the two pieces together out of a heavier yarn or am I intentionally complicating my life?

It’s certainly possible, generally you’d have to match the gauge, or adjust for the difference in yarn. As you observed it may complicate things. Other alternatives to that would be to sew a solid piece of cloth to the inside as well. The third option, and probably the simplest is to wash the hat a couple of times following the washing instructions for the yarn, it will generally take the roughness out of wool.

Hi and wellcome!
Lining the hat sounds like a geed idea for adding extra warmth as well as making the hat gentler on the skin. Rorshach is right that washing may well soften the wool, too.
I like the idea of using the sport weight for a liner. It’s a lighter weight (23-26sts/4") than the DK (21-24sts/4") and you’d like the liner to be [I]slightly [/I]smaller. Try a gauge swatch and see how much smaller the liner would be. If the lighter weight yarn makes the liner too small, add enough sts to adjust the size to what you’ll need.