Frank II, definitely go with compressibility.
I bought one of these, and have been very satisfied: HOMIEE Ryanair Personal Item 40x20x25 Travel Bag
It measures 40 cm x 25 cm x 20 cm and weighs almost nothing when empty (specs say 1.5 lbs). It can be cinched down to about 3"-4" thick if empty.
I've been quite happy with this bag, and it has worked perfectly for the way I use it, now across a half-dozen trips on some of the world's stingiest airlines (when it comes to stated limits for the small personal item aka "SPI"). It holds a lot (when not cinched down), is comfortable, with well-padded shoulder straps, and has proved durable, and even when loaded with heavy stuff is comfortable enough to wear as a day pack for hours. It's laughably inexpensive ($30, currently discounted to $21.29).
My approach to the small-personal-item dilemma was adaptability/compressibility, since, based on my research and experience, it appeared that airlines take such an inconsistent approach to this item. Some airlines officially set seemingly impossibly small limits on it's dimensions (especially the thickness, like a laptop sleeve), but from reports it seemed that enforcement of those limits is wildly inconsistent. I had upcoming travel planned for several airlines whose published dimensional limits appeared impossible to meet.
My strategy is this: Since many airlines specify maximum dimensions but do not specify a maximum weight for the SPI, I put all the small and heavy stuff in this bag (batteries for electronic devices, powerbank, DSLR camera and lenses, gold bouillon, bricks, etc.). Larger but less dense items go in my carry-on (I use a Rick Steves rolling carry-on). I leave the SPI bag uncompressed. But I am prepared to cinch it down as much as I need to if they enforce the very-thin minimums. Fortunately, I think I've only had to do that once (sorry, not 100% sure which airline actually required that, IIRC probably Lufthansa). Every other time, the heavy little bag has sailed through, un-cinched, without anyone batting an eye.
So what do I do if I get to the gate, and they give me and the un-cinched bag full of batteries and lenses the stinkeye? I have two words of advice: Cargo Pants. (Yes, I am serious). And a jacket with big pockets. I can pull enough of the small, heavy items out of the bag and transfer them to pockets distributed on what I'm wearing, cinch the bag down, pass muster, and board the plane.
While it's not particularly comfortable to be wearing a bunch of batteries and camera lenses in pockets, remember: you probably only need to do that for a minute or two, as you pass the scrutiny of the gate staff, walk on to the plane and take your seat. Then it's usually possible to offload some/most (maybe all) of the uncomfortable little bricks from your pockets and put them back into the small personal item bag (discreetly if necessary, but IME the only scrutiny typically comes at the actual doorway when passing through the gate; not much attention is paid to the contents of passengers' pockets once they're on the plane). While this is not an ideal configuration for comfort (and can look ridiculous), I've only had to resort to this once (out of dozens of flights I've taken since adding this bag), and in that case, only had to suffer the Big Pants for a couple of minutes. Once seated, I was able to re-distribute things easily and without inconveniencing anyone (the flight was half-empty with oodles of unused space in overhead bins). If the plane and the bins had been jam-packed full, I would have had to suffer a bit, but these flights tend to be short, not ocean-spanning. YMMV, but this strategy has worked for me.
Some who have more of a fashion sense than me might balk at the look, but I'm OK with it.
Hope some of the above helps. Cheers.
