I wish I had a real double boiler, but until I do I have found various ways to make-do. The simplest way is to take a very small sauce pan and place a Pyrex serving dish with handles inside it. The only problem with this method is that I don’t have a combination that’s large enough to melt more than an ounce or two of chocolate. It’s also a little hard to stir the contents since the inner pot tends to move around freely. With steam bubbling up around the edges, holding it can be awkward.
An alternative method which works a little better is to use two sauce pans and a simple sturdy binder-clip of the kind that holds a large stack of paper. You set one pan inside the other and clip the far edge of the pan to the other pan with the clip to hold it above the water in the outer pan (did you get that?). You can grab the handle of the pan for stability. The only drawback is that the inner pan will probably tilt slightly (instead of laying flat) and things will pool there. But for thick stuff like chocolate or caramel it works great! See the pics below.