Haven't done a backpack, but I do have a couple of leather laptop sleeves for the M#Airs. One is from scrap napa furniture leather (1mm chrome tanned), so it's soft and colorful, but doesn't protect as well. The other is ~2mm natural + pull up leather, so a bunch stiffer, to the point of being difficult to get the laptop in the first few times it was used.

Both of these sleeves are vertical envelope style, with a tucked tongue closure, and they're generally carried in some other backpack/bag. So these are basically the padding. They replaced _really_ low budget bubble wrap envelope laptop sleeves.

What I'd say from observation of the crafting/development process is that you're going to do one to figure out the issues and one to fix them all. (Or more, having seen a bunch of shoes made in my dining room)