3/8 might work but I would get 1/2. One thing I would suggest is always go with the 3:1 shrink rather than the 2:1. Its worth the few extra cents IMO.
3/8 wouldnt be bad to have on hand anyway. Personally I would pick up a couple feet of each. I learned my lesson on making cables on the very first pair a couple years ago. Always order twice as much as you think you might need.