I have a black LB that I would describe as light to medium weight, but the lightest I've ever seen were actually an LV from Anthem SS11 and an LP from Naska SS12; they were both very thin, sort of like paperweight leather. The SS11 LV was soft and smooth; the SS12 LP was soft but dry-ish (it was described as "washed blistered" leather in the description from where I purchased it). I also found these two jackets to have shorter sleeves compared to other two I own, by about a good two inches. (This was a serious downside for me as I'm 5'11".) They also seemed to run a bit smaller and shorter in general. (I could put 40 in the SS11 LV on, but it was way too tight in the shoulders to move much. The SS12 LP in 42 was still slightly tight in the shoulders, especially when zipped up. Both were shorter in length than my LB, which I love the fit of.)
As a side note: I found the LP leather on the SS12 interesting since I have a slightly older LP jacket in Dark Shadow (this particular shade is like a dark brown), that is a thicker abd has much more substantial leather (much like the hammered lamb description I've come across reading this forum). I'm not sure on the season of that one, however, but the style code is RP 4713 if anyone is able to tell me! The LB I have is from SS12, I believe, since the code on the tag is RP 3708 like the SS12 LP, although as I mentioned above, the fit is quite different.
Hopefully this will help you, or anyone else that has to buy online. I bought the Dark Shadow first, and must have just lucked out when it arrived and fit perfectly and the leather was just what I wanted. When I decided I wanted a black one, it took me three tries and several headaches trying to learn about and sort out the different leather codes and seasonal differences (fit, leather, color, etc.). At first I didn't know to ask about these things, so I could have saved a lot of time and money. There really should be some sort of comprehensive database! Especially since websites aren't always obvious about the season/type of leather. I've noticed Barney's and NAP to be particularly guilty of this. In the end though, I couldn't be happier with my black LB, so I suppose it was worth it. Here are some images, too; I had a hard time finding stuff like this in searches!
Okay...well I will post pictures separately. This is my first post and I'm kind of confused about the attachment feature!