Everyday Functionalty with PureOS security

This may be asking to eat my cake and have it too but asking doesn’t hurt.
I have run into a few issues with PureOS that other OSs support. I understand PureOS is locked down and open. One of the issues with 3rd party apps I have run into is with something I use for work. So my question is if there is a way of including repo’s into PureOS or if another OS (Ubuntu) would allow me to compile Coreboot and use the other security features being built for the Librem13?
Running a distro of choice on well put together hardware that just works justifies the machine by itself but if I can also use heads and nitrokey with a distro of choice that would rock!
Anybody know if Nitrokey will be OS dependent or work on a lower level? heads?
Is there another distro that allows for compiling Coreboot?
Is it possible to add PureOS repos to another Debian based distro?