I have similar needs and found a very inexpensive, technically easy, and low risk way to meet these same needs. Keep in mind that with Windows, your privacy is not even worth attempting to maintain with respect to Microsoft, the government, and skilled hackers. When I use my Windows OS, I never do anything I wouldn’t want to share with the company management anyway. So here is what I did. You can use the Librem Mini instead of the second NUC like I did. That would be an even better setup than what I have now because the Mini is much more secure.
1.) I bought two NUC6 PCs. Each one is the same size and shape as a Librem Mini and cost around $350 each when loaded with RAM and an SSD drive.
2.) Then I bought two monitors and plugged both NUC6s in to both monitors. Each NUC uses one monitor as the primary monitor and the the other monitor as secondary monitor, each opposite from the other NUC PC. Each NUC sits directly below its respective primary monitor. I leave both monitors turned on all of the time. Whichever NUC I boot has access to both monitors. If I boot them both at the same time (within a few seconds of each other, easy to do), then each NUC has only access to its respective primary monitor only. I have a third input to each monitor that allows for convergence using my Samsung Note 9 DEX, and soon, for my new Librem 5.
3.) I bought and installed a four-way switch that connects to a single mouse and keyboard and that breaks-out to each NUC and to my DEX/LIBREM5 convergence cradle. All of the cables are underneath my desk with a single thin cord with a single button on it, leading to just above the keyboard. Each push of that button rotates the keyboard and mouse to a different NUC PC or to the convergence cradle.
4.) Then I put Windows 10 on one NUC6 and Ubuntu Linux on the other NUC6. I keep a second keyboard and mouse in a drawer. When I need both PC’s at once, I plug the second keyboard and mouse in to one of the PCs.
This configuration takes up very little desktop space. Most of the spece is used for monitors, even the new thin ones, and the keyboard and mouse. Each PC is just big enough to plug-in USB cables to the front side if/when needed. Since the PCs are not connected to eachother and do not share hard drives, both PCs are safe from the other when used at the same time. Most of the time, only one PC is on at once.
Instead of using a second NUC PC, you could use a Librem Mini with the Purism factory configuration. When sitting next to each other on your desktop, the Windows 10 NUC and the Librem Mini will look like a matched pair. You could buy a more expensive NUC (maybe a NUC7) if you do a lot of gaming or video editing. But the NUC6 for a Windows PC gives me more than I need for office work and video conferencing.
I keep everything personal and creative on my Ubuntu NUC6. I do most of my business on my Windows 10 NUC6. The convergence cradle Works for Samsung DEX and I plan to use it for my Librem 5 once I get it. This configuration is also safer and easier to maintain and to experiment with. If I want to try something risky with either OS, I can swap out the hard drive of the given PC (Windows or Linux) first and put my original hard drive back in afterward. These little NUC and Mini PCs are quick and easy to open and make changes to. By keeping everything separated, you’re more free to do things that would otherwise risk everything.