Can you help me with a MIDI trigger?

Hi,

I am trying to make a project where I program a sequencer (hopefully not by using my computer as the end product, but in the process is fine) with songs, and then by using a singular trigger, one can play back one note to the song each time you hit the (only) trigger. Also, I want the participant to be able to simply, with a button, choose from a couple of different songs. I am lacking a sequencer outside of my computer, so I will need to get one. Does anyone have any ideas as to what kind I need or if it exists, or if a toy or something already exists like this (which I would use.) Thank you for your help!

Dana