No specific recommendations, but I don’t think you need to spend a lot. Sounds like you don’t need USB, just an analog mixer. For the A4, all you need is one stereo channel (or two mono channels). If you want to combine other instruments, factor that in, too. Always get a few more channels than you think you need though so it’s not obsolete too soon.
The stereo channel on a mixer might be two 1/4" inputs, or a single stereo 1/4" input. It’s best to find one with separate balanced 1/4" TRS inputs since the A4 supports that (it reduces noise especially over a long cable length). In that case you’ll need 2x 1/4" TRS cables (the kind with two black stripes). The single XLR inputs are usually mic preamps.
Also look for something with separate outputs for monitoring and recording. Usually there are main outputs you could run to a Zoom (or tape or whatever), and then separate outputs you can connect studio monitors too, and then also a headphone jack.