Dear Norah,
I have always hand-quilted my quilts and have always had the same concerns about it that most folks seem to. I spent years fretting about it until I realized that it just simply doesn't matter that much.
Stitches that are small enough to fill their primary function which is to support and stablize the layers is good enough, at least to that extent.
Small is fine; even is better and is now my first aim..also realizing that "even" should include the larger stitch size that comes when you are stitching thru a seam line,with extra layers of fabric to contend with. Stitches 1/8" long, or slightly less suit me just fine.
Besides, I've always thought the larger stiitches look cool and more "quilterly". With crippled hands, I'd rather focus my forces on perfect piecing; that's a battle I CAN win. Hope this helps.
Mary