Playing alto 2 1/2 years
The widest choices will come with using an actual mixer, such as this one:
Especially with a Mac, this will solve all the problems as well as provide phantom power if you get a pro mic that requires this. As said previously, getting the signal into an iPod or phone is a different story and listining to a backing track would need earphone I think. Or, a little more firepower (channels, EQ, more inputs)
Behringer Xenyx 302 USB, 5-Channel Recording and Podcast Mixer, 1 Mic input with phantom power and peak LED, 1 Stereo line input, 2-Band EQ in both channels, 2-Track in-/output, Master fader, 15 V phantom power, USB...
Behringer Xenyx Q502 USB, Mixer, 1 XLR Mic Input with 15 V phantom power and compressor, 2-Band EQ and peak LED, 2 Stereo Line inputs, 2 Track In/Outs, Master fader, USB Audio Interface, External power supply