For a bag, I bought this a few years ago and it has been great:
https://store.ricksteves.com/shop/p/carry-on-backpack
It soft-sided and doesn't have a rigid frame, so it's easy to squeeze into the overhead. It doesn't have wheels, but it does have stowable straps that let you carry it like a backpack. I use a shoulder strap instead because I don't like it being behind me where I can't see if someone is messing with it.
What I like about this compared to a regular backpack is it lies flat and folds open like a regular suitcase. Also, it doesn't have rounded edges like backpacks, so it maximizes the interior space in the carry-on size.
It has ample pocket on the front for easy access to things you need while you're in-transit while keeping your clothes safely in the main compartment.
Not having wheels can be annoying when you're carrying it around, but it encourages you to pack light. Also, in old cities in Europe, the uneven sidewalks and cobblestones can be a hassle to navigate with wheeled luggage.