I've dabbled in Eagle before... usually making slight tweaks to already existing designs. I'm designing the bracelet PCB from scratch. The first design was.... lacking.

I knew the first design would be large, but not so large that it wouldn't easily fit on a wrist. There are a few reasons for the size:

• I'm using larger SMT and Through Hole components, because I planned to solder everything by hand. 
• I did a really poor job arranging the components on the board
• I have a number of large programming pins

I'm in the process of creating a second design - where I'm planning to reduce the size of the components and switch to SMT for most cases. I'm also going to revisit my programming headers.

I might start with one of the Adafruit Trinkets as a starting point... at least some of the components (Cortex M0, Caps, and Voltage Reg) are already laid out.