for what it wants and needs to be i think purism has made the honest choice regarding producing a libre smartphone device with only single sim on removable m2 card. considering their constraints on hardware and software design they have made a pretty good job with some exceptions regarding the battery.
a real dual sim ( simulataneos dual-network ) is a rare find and is not as energy efficient as a single sim one. the main reason beeing in that it has to simultaneosly send/receive on both networks thus making everithing a convoluted mess.
if you need to separate business from pleasure the obious choice would be two separate devices that allow you to remain active throughout the day without worring about battery life. if space and differentiation is a problem use smaller phones with different colors or different bumpers.
blackberry is a beast in that department because they have those sweet phone holsters that you can keep on your belt and are general work horses even if they are a little old (the physical keyboard type-ones with the hot-swapable batteries).