We keep the house pretty cool during the day, and sometimes it is around 64 degrees. So we need sleeves for naptime, or I guess I could nap the littlest one in more clothing under a regular sleep sack.
To make a new sleep sack pattern, I took an existing sleep sack and a long-sleeved t-shirt and set them on top of some construction paper. I put the construction paper (blue here) on the halfway line of the sleep sack, and cut around it, adding a bit for a seam allowance on the edges.
For the sleeves, I cut a full sleeve around the shirt that fits.
If I didn't have a sleep sack that fit, I could have just used the t-shirt as a size model and added length and width by either measuring my baby and adding 6", or by putting pants on the bottom to estimate the right length, then adding 6" for growing room.
After making the pattern, I cut my pieces.
I cut the back using the big piece. I meant to cut the front the same, but as you can see, my fabric wasn't big enough. So I took as much as I had and cut it. Then I took scraps of the other color and cut them to fit the top part, adding for a seam allowance.
I cut the sleeves next.
Then I went back and laid the sleeves on top of the bodice. I cut the bodice inwards to estimate where the sleeves would need to be sewn and so that the sleeve top was the same shape as the bodice attachment area.
Then I started sewing. First, I attached my front pieces to make one front piece.
Then I added the zipper (a separating zipper sewn in upside down for easy diaper changes). One one interior side, I made a zipper protector, or flap. This is to keep the zipper from touching baby's skin and irritating him. I did this by cutting a piece as wide and long as the zipper from the inside. Then I stitched it on, making my stitching line hit where topstitching would. Then I topstitched around the other side of the zipper.
Next I attached the front and back bodice pieces at the shoulders.
Then I pinned and attached the sleeves around the bodice. Next I turned it inside out and closed the sleeves and then sewed around the whole body.
Then I turned it right side out and made sure my stitching was secure. You could finish the sleeves and the neck, but I didn't because fleece doesn't fray.
I love it! Works great!