Go for a 15-inch if you travel a lot - it's barely heavier than a 13-inch but you'll definitely gain comfort working eight hours straight. That extra space is really nice when you need to see multiple windows at the same time. That said, if you're constantly on the move (trains, planes all the time), the 13-inch stays more compact, but yeah, it's a trade-off on ergonomics.
For brands, you can look at ASUS, Lenovo or ViewSonic - they all make solid portable models with USB-C for both power and connectivity at the same time. Look for something with a good panel (IPS preferably for viewing angles) and a case/stand included in the package. Just make sure to check USB-C compatibility with your laptop - sounds obvious but it needs to be compatible for it to actually be portable. Avoid the cheap unknown brands, that's where you get burned on screen quality.
Real talk: check reviews on review sites, not just Amazon stars. People actually speak their minds about durability and how it holds up after a few months of travel. There are models that have a good reputation for standing up when you're lugging them around everywhere.