Check out r/rawdenim, filter search for denim jacket.

If you want BIFL quality, you are going to want a selvedge denim material (I'll let you research that, basically it will last MUCH longer), and likely denim around a 13 ounce weight.

The cool part about buying a raw denim jacket (evenly and heavily dyed, straight from the manufacturer) is that the denim will develop creases and fades around your body, creating very personalized fades over the years. Way cooler than buying some pre-stonewashed H&M jacket that will blowout in a couple years.

The best denim (arguably) comes out of Japan, because the last American denim mill just closed its doors a few weeks ago. Many North American companies purchase Japanese denim, and manufacture the garments themselves, like 3sixteen (too pricey for me), Naked & Famous (if you like big tiddies on your jacket patch), and others.

I'd recommend buying a made-in-Japan selvedge denim jacket. Measure a coat that currently fits you well, and find a website that offers online measurements with their products. Japan's gonna run a little small with their sizes.

I'd recommend Okayama Denim as a starting point. You just missed their 17% off sale, but theyve got a great selection at competitive prices (compared to brick n mortar shops in Japan). They also do free returns and exchanges in case something doesn't fit.

I just dropped 200$ on a Burgus Plus Type 3 black trucker jacket... cause I'm gonna wear it for the next 20 years! Buy quality, buy it for life.

(Type 1 and Type 2 denim jackets fit roomier and slightly boxier than the standard Levis jacket, which is a Type 3 by the way. They're based on historical Levis and Wrangler models, they may fit the bill for you).