Definately don't take the cotton long underwear. You need either wool or synthetic. Target, Walmart and most sporting goods stores sell something that will work. Target's brand of sythetic clothing is Champion and is often labled DuoDry.

Look into new insoles for your boots like superfeet or possibly using an arch support like Tacco. I have wide toes, narrow heels and a low volume foot so adding an arch support helps my shoes to fit. You can also go to a good backpacking store with your boots and ask to be taught the different lacing methods to 'lock' your foot in place.

Hav Fun