Just go for a Hirsch strap. They got you covered.
Either of these should work for you -
If you want something a little pricier, but also higher quality, try these -
Would Horween-Cordovan work? 2.5 to 3mm thick. Made in Germany with fast shipping.
I have a black (first quality) 20mm wide (shown here). Around 72 usd.
I also, have a brown (2nd quality) 20mm wide. Around 42 usd.
Can't really tell any difference between the two straps in quality.
They measure 118/75mm.
Trusted ebay seller. I noticed a few of these on the forum. They get good reviews and the out of the package inspection sure looks good.
So, far I haven't mounted mine because there's only six holes on the tail, so I may need to add a hole, or two, toward the lugs to accommodate my small wrist (not sure yet though). That's why I'm including photos with detailed measurements referencing not only length, but, where the holes start and terminate.
Best of Luck in your search!