Need recommendations for a wwan card

I’m looking for a wwan modem for my laptop.

i am not an expert in this field and have no idea what makes a good wwan modem and what are signs of garbage quality, hopefully somebody here can lead me to a good product.

my only requirements are:

  • fits in the wwan slot of my Dell Precision M6800. (its just Mini PCIe afaik.)
  • must be compatible with T-Mobile’s LTE service in the US.
    *must work with Debian GNU/Linux 10 (Buster). i can install drivers and compile my kernel if needed.

i have already tried the Dell Wireless dw5808, which works fine, but isn’t compatible with T-Mobile’s LTE service, only 3g.
i have also tried the Sierra Wireless MC7455, which reportedly is compatible with T-Mobile, but it is not compatible with Debian 10, at least not on Linux 5.2 or 4.19.

You ever find anything? I asked around the office and mostly we use what comes in Dell or hp laptops. I’m not sure but it seems like the Sim slot is part of the chassis. These all seem to use software defined radios so you flash whatever carrier on it to make it work. None of them are great from our user reports apparently.

the sim slot is indeed part of the case in my laptop.
from what research i was able to do, it seems the sierra wireless MC7455 is the closest to something i need. i have one, and it fits in my laptop perfectly, it just renders Linux unbootable. it would take somebody much smarter than i to make it run on Linux.