Thanks, all! This is a great thread, with great suggestions. I will definitely look into a Goyard Artois (I love how it looks), and will also research the Senreve Maestra (which wasn't on my radar at all).
I've ordered three possibilities, all of which are preloved and two of which can be returned. The one that can't be returned is a Celine Edge bag in black and white. I had and loved this bag years ago, and while I didn't carry a laptop in it at the time, I know that it's tough as nails. I regret selling it, so when I stumbled on one is very good condition for a very good price, I snapped it up. It's a bonus for me that it is black and white (the same combo I used to own). I don't really do beige, and wear a lot of black even in the summer, so black and white is perfect for me in the summer.
For anyone who does do beige in the summer, I think this
Loewe Lazo on VC could be a really stylish option -
https://www.vestiairecollective.com...e/beige-fur-lazo-loewe-handbag-11566148.shtml. I can't comment on its strength, but I have a mini version of the Lazo in a different color, and it is a GORGEOUS bag.
The other two possibilities I've ordered (that can be returned) are a small Tod's Oboe Hobo and a small Celine Tri-Fold. My laptop is only 11.8" long, so both of these would work dimension-wise. I may be unusual in that I prefer the look of the Tri-Fold with the "wings" pulled in, and I'm concerned that carrying that way will eliminate a lot of space, but I want to give it a try.
Happy Hunting!