Sew with upholstery thread (furniture grade) for a strong hold. Use water soluble pen or chalk to draw the 1/4" seam allowance line if needed. When pulling thread to close the opening and tighten stitches, use a pin or needle to "ease" the threads down evenly so they don't tangle together.
♥ More videos in my How to Make Plush series: / teacuplion
☕ Full site, portfolio, and sewing tutorials: www.teacuplion.com
♥ Plush sewing patterns: https://www.etsy.com/shop/TeacupLion