I've been looking for one and I have the same concerns you do, and right now the only thing I realistically see if I want completely open is a thinkpad x200/t400 flashed with libreboot.
Nothing I do with secure data hard-requires that level of portability, and for insecure (tracked, DRMed, closed + signed firmware) mobile use a Lineage smartphone is good enough for what I do. A laptop with closed / signed firmware simply doesn't gain me anything worth having over the phone.
My personal desktop is a Blackbird. The couple of old x86 apps I can't easily ditch (because they are open source but need MVC APIs and I'm too lazy to write the shim layer) I just forward X over SSH to an old corebooted Opteron box.
Can you put a POWER "base station" of sorts in your dorm / apartment and use a low power secure terminal, like a corebooted C201, to access it over an encrypted link?
I've done something like this when I had to travel last -- was able to maintain a stable link back to one of my POWER machines so the lack of local computing power on the laptop didn't matter. Really hate that Chromebook touchpad though. ;)