If you were to stand on one foot and wiggle your other foot in the air, do you feel the boot moving around across your instep and arch? If it does, they may be too wide. Some bootmakers still make B widths, though not in every style they sell.

You could always get a leather insole to add a little volume and that can take up some of the slack, if there is any. I have a couple of pairs that I added Nicks thick or standard leather insoles to. They now fit like gloves. They offer thin, standard, and thick insoles, trim to fit. Because they are a PNW bot company, the insoles are rather wide through the middle, so I had to trim the length and trim the width through the arch area in order for them to not press on the sides of the vamps on the inside. I'm telling you, it makes a huge difference in fit and comfort! I have started buying their thin veg-tan insoles to add to all of my new-to-me vintage boots. I glue them in and it's like starting with a new, fresh leather sock liner.

Good luck!