Most people baste securely before STID to be sure that nothing slips. A 24 inch square quilt would need some form of basting. I have used Thermolan in table toppers and have done STID successfully. A walking foot is invaluable to success. It allows you to stitch all of your rows in the same direction whereas with a regular foot you have to stitch some rows from the top to the bottom and alternate rows from the bottom to the top so that you do not have the quilt pull out of shape. If you reverse rows and your piece is not secure it will distort the rows and they will not appear straight.