I haven't tried to sew it up, but I found this pattern here https://www.mimiandtara.com/dog-t-shirt-pattern/
Let me know if that works for you.
Posts by Krisandra Slye
I have a computerized machine with an LED panel, and one day my machine started back stitching at the start of every seam and I couldn't figure out why. Well, apparently it's a feature on the screen you can click on and off. I was amazed, it saves me time now.
I agree with Cat. It all depends on what type of fabric you are using and if the needle is made for that type of fabric. For canvas weight, or multiple layers of fabric (like when sewing up a handbag) I use a size 100/16 needle. For quilting cotton with just 2 layers a 80/12 will work just fine. Let me know if this helps.