Design your own lining: Lay your purse, tote bag, etc. on paper (or fabric if you're feeling confident. Draw around the bag an inch from the outside edge. Cut out template, then pin and cut two layers of fabric right sides facing. Sew a 1/4 inch seam around the sides and bottom, iron seams out flat (yes, you can "finger press", but ironing is neater), fold over the top edge 1/4 inch so that the right side is showing, press. Insert into knitted bag, handstitch (it looks nicer) lining to knitting. You don't have to stitch all the way through to the outer layer, so it won't show on the outside. If your bag is open work knit, cut double the pieces of lining, sew them separately, turn one inside out, place it inside the other and sew them to the top edge of bag as before. Voila! Your pretty lining shows through!
So your template formula is one extra inch cut out around the bag and 1/4 inch seam allowance. If you have a bag with height, width AND depth, use this method to make pattern pieces for all sides and bottom of bag. The extra 3/4" adds some "give" to the bag. If you're really tricky and you have a bag with a rectangular bottom, sandwich a piece of flexible plastic (like lightweight quilter's template), cut to fit inside the seam allowance, in between two layers of fabric to give the bag support.
You CAN use any kind of fabric for a lining, even very lightweight vinyl. But keep in mind that it's harder to sew slippery stuff.
Sewing For Dummies can help out if you are clueless about sewing. But if you are able to knit, ladies and gentlemen, you are definitely with it enough to sew! It's all about following directions.