Forget about asking for advice though, unless you can talk to people who actually own the bags. You need to SEE the ins and outs and size and fit of the bags..to that end i am going to post you some youtube reviews.
Here is ranking from someone who travels with every major indie bag in the buis.
Minimal Travel Hybrids:
https://matterful.co/hybrid-travel-backpacks/
I do have one piece of opinion/advice here. Chase lists the smaller hybrid bags (which seem to be what you are looking for) but rather than buy the mid size hybrid type bag....my philosophy is to buy the fuller size bags and just under pack them to make them lighter and use the various compression mechanisms to make them smaller. Given i literally have an entire closet full of bags i find it easier to compress a full size bag and to use for less packing but still have it for bigger trips if needed than to have to collect both mid sized and full sized travel bags. Be that as it may, you may strictly NOT be wanting any bags that ever do full size so if so, you can disregard all this part ii'm talking about right now and the list below. There is some merit to the more midsized, as if you are carrying even a compressed full sized you COULD still end up being asked to check it...especially on commuter flights.
More full size travel packs
https://matterful.co/one-bag-travel-bags/
Anyway, I use all of the above. If you don't mind the "im elon musk" the Nomatic Travel Pack (not the 40l travel BAG but the travel pack that is 20l compressed and 30L expanded) might fit the bill.
If that is too techi the highest rated bag in the buisness is the Peak travel bag which can go from 35L when compressed at the top to 40l in standard to 45L expanded.
Another highly related option would be the 35L sized Tortuga setout or the Setout divide (if you like more organization).
Tortuga: Not as waterproof but you can buy the water cover, you can also get a side strap for duffle mode....its light weight and with best suspension system in the buis. I am not sure if the 35L Tortuga has the luggage pass through (the 45l i have does not have one which is a bummer because it compresses down nicely).
Peak: Best overall, not cheap (let me know if you are interested and ill show you how to get a good discount), not as compressible as tortuga and nomatic. Very water proof, can also add water cover, best packing cubes in the buis. Probably the most amazing hide away for hip straps (and to a lesser extent, the shoulder straps) in the buisness. Also the only bag with side access on both sides and handles on all ends. Has the luggage pass through. No side satchel straps but that isn't really a con here.
Nomatic: Comes with it's own packing cube, also fairly water proof, no cover available. Has nifty features like built in key cable, sun glasses box, a some what usable "brief case handle" for side carry when compressed. Compresses to the smallest of the bunch while not looking compressed.
I also use the Tumi bags (I have the Nellis Alpha Bravo leather) and Travel Pro platnium. As you said, those are more like "book bags". I just keep one of everything and grab what ever i think i need given the weather and what i want to take and the kind of image i want to portray on the trip.
I own some of these bags so if you have questions let me know. Some other bags i don't own but i think are worth looking into are the AER Travel Bag and the Minaal. If you like that tactical look the Go Ruck
Ill post some reviews below.
https://www.youtube.com/results?sear...ic+travel+pack