Hiya
@Bogwoppit ... there are different kinds of hand quilting. If you want tiny stitches you need size 9" betweens" needles and a couple of strands of embroidery thread or thin cotton thread. You do tiny, rocking motion stitches. It's not easy until you get "into the groove"
If you want the stitches to be more decorative, use an embroidery or preferably a sashiko needle and either perle no8 thread or embroidery cotton. The stitches must be even, but size doesn't matter, it depends what effect you want to achieve. It is called "big stitch " quilting, although, as I say, the length of stitch is up to you and your design.
Hope that's helpful