If only glueing would hold it in place that would be great, I can't sandwich it between two pieces of leather as then I would run into the weight problem again. The way I was considering to do it would be to create a box shape like I plan to do to lining and then glue it to the sides and stitching it together at the top with the zipper and on the sides of the bag (shoulder strap attachment and handle attachments). But maybe I am overthinking it here and it would work just as well to attach the pieces seperatly on each side?
The bag is inspired by the Mulberry Clipper (https://www.mulberry.com/us/shop/women/travel/holdalls/clipper-oak-natural-leather), and I wish to retain a shape as such pictured also when the bag is empty, - more or less. I think the shorter sides would benefit from using the thicker .8mm and for the longer sides I was thinking I would go with .6mm of Texon. The benefit of creating a box as I see it would be to avoid qurky corners in the bag but maybe that wouldn't be a problem anyhow? I have the outer layer of the bag completed, the lining I will be using is very soft and will unfortunately not add that much to the structure of the bag. Maybe I can try to upload a picture of the box I have created for testing purpose and that might be more informative of what I am trying to achieve
I think they are actually the same product, just sold under different names depending on where you are located. For me, living in Europe, it was sold under the name Texon. I would say that both the .6 and .8 are about as stiff as a 2mm veg-tan leather (very roughly), I can imagen that the 2mm is quite stiff and maybe in my case would be more suitable for the base of the bag as I believe you used it. I will update the thread if I decide to use the texon!