Hi @murphtc I think that the fit of the shirt is a little bit of personal preference; however it is designed to be worn as your first layer, then you could add on top of it.  If being worn as a second layer most people wear it unbuttoned.  If you still decide you want to go up in size I suspect that it will still look just fine.  Your trips sound awesome, have a great time!

At REI, we believe time outside is fundamental to a life well lived.