Let's start with the Army. These have been my go-to winter pants for several years now. They wear like iron. They never look dirty, and water actually beads off of them! I know this because I tend to wear them for a week at a stretch, even out to do chores. I wash them on the gentle cycle and hang to dry. For those extra cold days, a pair of silk longjohns underneath is perfect.
I would suggest purchasing a size that is no more than two inches bigger than your actual waist measurement. This will make the alterations easier.
|inside view of the centerback seam|
For these I simply took the extra width out of the centerback seam. Take a bit more at the top of the waistband and taper down into the crotch seam to ensure a smooth fit.
My sailor pants are new to my wardrobe and just as comfortable. However, anyone familiar with these pants know that there are so many flaps and buttons and pockets and lacings going on all over the waistband, it's nearly impossible to find a clean stretch to nip and tuck.
|inside view of the dart|
Again, don't purchase a pair that is excessively large because there just isn't room to alter away that many inches. After considering all my options, I decided on a short dart on the outseam. I took a 1/2" dart at the waistband and tapered down five inches. This dart falls just between the front buttoned flap and the back welt pocket. The dart adds a nice shaping to the hip and doesn't interfere with the structure of the pants.
Whenever you're wearing vintage, odds are you'll have to do some amount of alterations. For me it's typically shortening hems and sleeves, or reshaping darts or side seams because I'm short-waisted. But making small allowances here and there can really make a difference!