Looking for tips on making simple Midi controller standalone

Hey everyone,

Yesterday I created a program on Arduino for sending Midi program change messages to my synth. Everything came out great, and now I want to work on freeing it from the Arduino programmer. The I/O is super simple with only two digital ins for buttons, an output for an LED, and the serial port for digital communication over midi, so obviously I don't need the power of the whole ATmega chip. I've been trying to figure out my options for making a compact, battery powered version, but I've had a lot of trouble parsing the information online.

It seems that some of the ATtinys would be able to fulfill my needs, but I can't tell if they will be able to communicate over serial like the ATmega in my Uno board. I've also read some things about using internal clocks as opposed to external crystals. The midi spec requires serial communication at 31250 bits per second. What bearing does clock speed have on midi communication or battery life?

Overall, my major concerns with the project are low cost, small size, long battery life and low power consumption, and low complexity, in that order. Any advice on how I can achieve these goals would be great.

Thanks in advance.

Maybe this can give you a headstart.