That's your best option. I used this one: https://www.amazon.com/BCW-Supplies-Stor-Folio-Comic-Comics/dp/B002AT8QKU/ref=mp_s_a_1_3?crid=LUGH1BJ9HBUA&keywords=comic+stor-folio&qid=1652609867&sprefix=comic+stor%2Caps%2C87&sr=8-3 Sturdy and keeps them nice and flat. Just don't be that guywalking around with your books in a Samsonite luggage rolling suitcase 😆
Hex Brand did a backpack collab with Jim Lee that has dedicated pockets for books, so it may be worth looking into. I actually bought one at SDCC this year, and the bag was light and comfortable enough to carry around all day during the con. I didn't use the book compartments because I still had a book carrier on me the whole time, but I personally wouldn't use them for raw books - they seem better suited to slabs due to their size. Raw books would have a lot of room to move around in those compartments, so dinged edges/corners wouldn't surprise me.
If you don't already use one, you can get a book carrier (like this one) and just carry it around in any bag you decide to go with. For past cons, I've just carried one or two of these in my backpack, and any raw books or smaller figures that I bought have stayed protected in them.
As for specific bags, I recommend Chrome Industries. Really high quality materials, and also weather resistant. Their bags can get pretty pricey, but they've had really good deals on Black Friday in years past. Only catch though is that their bigger bags can get pretty damn heavy even when empty, so if you want to try one of theirs out, I recommend going with a smaller bag.
On a side note, I'm not sure if SDCC still did it this year, but in 2019 and earlier, they had a bag check in the convention center's main lobby. If they are still doing it, that could be another option to avoid carrying stuff around all day. I bought a bunch of exclusives from Hasbro in 2019, and they just give you a single huge bag that is super uncomfortable to carry around; bag check came in pretty clutch.
I have one of these as well and I would highly recommened them. I don't think it's waterproof though.
http://www.amazon.com/BCW-Supplies-Stor-Folio-Comic-Comics/dp/B002AT8QKU
If only there was something like this for manga.
Alternatively I would recommend these: http://www.amazon.com/BCW-Comic-Book-Storage-Portfolio/dp/B002AT8QKU/ref=sr_1_1?ie=UTF8&qid=1420382080&sr=8-1&keywords=comic+book+stor-folio
There are "carrying cases," like the BCW Comic Book Storage Portfolio. However, you really don't need those.
I've traveled all over the country with comics and have never used anything more than bags/boards.
Usually, I'll just bag/board my floppies and then put something of a more substantial size on both sides (i.e. a hardcover book or something of the sort). I've also rubberbanded them together, although I'm not a big fan of doing that. Lately I've been packing stacks of books into the brown paper bags I get them in at my store, and then tape the bags shut to keep them tight.
I have never had a real problem with either of these methods. If you want to spend extra money, you're more than welcome to, but it really isn't necessary.