Have you tried working a knit-in pocket? Before you start, it's a little abstract, like trying to visualize an origami animal without a piece of paper, but once you get there it all falls into place.
I think I will expand on this post later with some illustrations, but for now just words.
From the bottom up, a horizontal knit-in pocket is made like this: make your pocket lining, usually a rectangle, and put it aside without binding off. Next, work the sweater to the position of the top of the pocket opening. Then on the sweater, work to where the pocket opening begins, bind off for the top of the pocket opening, and finish the row. Your stitch count will be down by the width of your pocket.
Now is the part where it comes together: put your pocket lining on a spare needle, and on the next row of the sweater, work to the bound off pocket opening, and then work across the pocket lining, and then work the rest of the row.
You'll be back to your full row stitch count, with a rectangular flap of pocket lining hanging off the back of the work. Then finish the sweater as usual. The pockets get sewn in the finishing process.
Before you block, that pocket lining might seem impossibly curled. The bound off pocket opening might have a loose stitch at the side where you joined to the pocket lining.
The whole scenario can look a little hopeless; how are you going to turn this into a nicely finished pocket?
Start by blocking. That takes the curl out of the pocket lining.
Then, take a couple of dpn's and mark the lines where you're going to attach the lining as follows: from the right side of the sweater, carefully thread a dpn over and under every few strands between two columns of stitches, at the sides of the pocket opening where you're going to attach the lining. Those two dpn's will guide you while you're stitching the pocket.
Pin the pocket lining in place between the dpn's. Thread a blunt yarn needle and whip stitch the lining to the wrong side of the work, matching every second row of the lining to every second row of the sweater. You can slide the dpn out as you go if it gets in your way.
When you finish one side, use a dpn to make a horizontal guide at the bottom of the pocket. Stitch across the bottom, matching stitch to stitch, and then up the other side of the pocket lining.
If you have a loose stitch at the edge of your pocket, use the tail of the yarn you used to sew the lining to carefully make a duplicate stitch over the loose stitch and tighten.