I've been working on sewing some trousers and a shirt. From these projects I learned that the strongest hand stitch traditionally used for sewing clothing was the "back stitch." Basically, on the front of the fabric you take a small stitch backwards. Then, on the back of the fabric you take a large stitch forward. The forward stitch should be twice the length of the backwards stitch. Now take a second small stitch backwards. This stitch should enter the fabric where your last stitch on the top side ended. If you google back stitch you will probably find some examples that make more sense than my explanation. Your other option would be to just use the saddle stitch. I'm not sure if it was traditionally used to sew cloth, but I don't see any reason not to use it if you want to. Good luck!