I have an old Singer and an even more ancient Pinnock (small industrial). The Singer copes with denim as long as I go slow on the tricky bits and use a denim needle (changed regularly). Before sewing I pound the thicker bits then give them a good press, keeping the seams open. It is not a quick process, so don't be hard on yourself. If you get really stuck or worried you could hand stitch using a sharp mattress needle, but you'll be ok if you just stick with it. Let us know how you go and post some pics.