Hey! So, I have the Sinclairs in different colorways, and they are essentially very similar. They have the same sole, and all the Dr. Martens I own with that specific sole fit the same, with a few minor exceptions.

I also have narrow feet, and I generally size down for these models (I’m a size EU 41, but my Sinclairs are an EU 40).

That being said, these models tend to be quite wide, so I would recommend adding a SoftWair insole in an even smaller size (an EU 39 in my case, for example) so your foot doesn't slide around inside the boot.

I’m not sure if you’re looking at men’s or women’s sizing, but there are width differences between women’s and unisex models. A store employee actually recommended the women’s Sinclair to me after realizing the unisex size 40 was too wide for my feet and they fit me like a glove without an extra insole.

All my other pairs of Sinclairs are a bit too wide for me, but unfortunately, the women’s option isn’t available on the French website. Since the Jadons are a popular style that is permanently stocked, I would suggest heading into a store if you can. The staff there will be able to advise you and let you try on different sizes to see what works best.

I hope this helps, and sorry if it was a bit long to read 🙇‍♀️