I made some winter pjs for Big W in my post-baby sewing kick (thanks to my maternity leave). I used Simplicity 5317 for both the top and bottom; the top is supposed to have snaps at the shoulder, which I left off. I meant to compensate for that when I sewed it, but the neckline is so big on him, I think I might have forgotten too. Oops. It's pjs, so it isn't such a big deal. The top is a little short his long torso, but the pants fit great.
I used a waffle knit I found at Girl Charlee for the top. It has little cowboys and stars, and it's just a little thin, but Big W gets warm easily, so it should work. If not, then I'll just use a long sleeve T instead. The pants are made from a flannel I found at JoAnn's, in the remnant bin. If you have a very small child and a large remnant, you can get away with this, and they're always at least half off. Bonus.