I want two laptops in one body

I don't know how practical this is on Apple hardware (I don't deal with hardware much overall, I'm a software guy), but in general, you can usually get by with just two SSDs/HDDs, each with a different OS instance on it, to separate work and home. Assuming, of course, your company would allow you to modify your work machine, if they gave it to you. A physical switch is pretty unnecessary, as you couldn't switch between systems without cutting power to one anyway (and basically nothing is stored outside the hard drives anyway); choosing a drive/OS on boot should be fine.

One answer is to have the work "laptop" be a cloud desktop. This is a popular choice for firms (say the Bridgewater hedge fund) that are paranoid about computers falling into the wrong hands.

I use two different logins. One is my "Writing Room" with no access to the internet or...the internet. Just Sublime.

The other login is all the stuff and work.

I like the Writing Room.

Keep in mind that many employment contracts and much labour law considers work performed on the employer's equipment to be the property of the employer.

Technically, a hard-drive swap would address most of your concerns. (There remain risks of hardware / bios keyloggers and other surveillance tools.)

Either get a cheap notebook for yourself, or leave the work box at work, and explain your rationale.

Couldn't this be accomplished with a hypervisor and 2 virtual machines?

I had a second hard drive attached to the side of my laptop and ran it in a virtual machine that is the closest I have gotten.

Multiple user accounts/logins. You can move one or more of the /user folders to an separate disk if you want.

How about carrying an USB-C SSD with VMs on it? You can have however many switches you want, not just one.

Dual boot?

you want one physical computer with two logical computers - dual boot.

duct tape