look into this one, try to buy on app, there is some tap and win discount which is available only on mobile.
As per desidime, this one has extra m.2 slot too for storage expansion and it mentions upgrade till 40GB, which means the SODIMM slot can take 32GB, but that would disable dual channel. Still 16GB should be more than sufficient for the kind of usage you described.
As far as memory going bad, that's not a concern anymore, at least in the last half a decade. But yeah, replacing a soldered ram is not ideal even with the manufacturer warranty. But I would again point that in modern computers, memory failure rate is very very small, almost negligible.
As far as isolating the bad ram goes, it's complicated. So if you want to isolate the whole ram, then you would need some wizard level desoldering and soldering skills, also you need to have a unit which is sold in millions all around the globe, so chances of finding a manual on board repair is easy. Since the soldered slot is slot 0, you would always need it. But with skills, maybe you are able to connect the slot 1 to slot 0.
But usually every modern (linux and windows, no idea about mac), allow you to isolate bad areas of a ram module. So you can find and isolate bad areas of the ram in slot zero, which will bring the total available ram lower but would stop causing an issue.
https://thecomputerperson.wordpress.com/2015/04/20/how-to-block-out-or-map-out-bad-ram-in-windows/ this is kinda old but last note is from 2022.
At the end, if your concern is soldered ram going bad, then you need to step out of thin and light, maybe look into under 55k gaming laptops, those usually have enough space and thus easy to find non soldered ram slots.