Using garageband with two USB inputs

I have a USB microphone and a USB guitar cable. I want to EASILY be able to use these two things to record the guitar and my voice at the same time in Garageband. I know there is a way to create a dual input using settings, but the Mac doesn't remember and I have to redo it each time and I can never remember how to do it. It is very frustrating, involves multiple steps, and by the time I get it set up I've lost my energy for recording. Is there an external mixer or something that will simply connect via USB to the computer and allow me to connect my USB inputs to it and that be that? Any suggestions would be appreciated.