except maybe an open source hardware wallet where other, tech-savy people, would dig through their code
That kind of hardware wallets start to gain more and more ground lately. Even the old "established" Trezor is open source (just it doesn't have Secure Elements chip yet). A list is here:
https://bitcointalk.org/index.php?topic=5304483And if a HW is open source for, let's say at least 6 months, I am 99.999% sure that multiple tech savvy people have checked it over a couple of times.
Hopefully my Ledgers won't break down on me so I don't have to buy another hardware wallet ever.
I don't realistically have such hopes. Sooner or later it
will break, but I guess that it won't happen for at least 5 more years. My hope is that the technology will be better and cheaper until my HW dies off.