If you own a Windows 7 install dvd, that is not tied to a specific computer, you can use it forever.
The newest processors don't support Windows 7, however, They don't support Windows 8 either.
It should be possible to get up to 5th generation intel processors and the older qualcomms and amd for some time, but you will have to shop around and might have to get them used. Processors that are well kept (computers kept clean and paste and whatnot doesn't get in them) last a long time.
You can get refurbished boards and processors.
If you don't own Windows, your best bet is to get refurbished computers. I work for a company that sells a lot of them, online and in store. Mostly old Dells, which are a good, well made computer brand. You can still get them with Windows COAs.
You can also buy the newest processors and boards, install a Linux version like Ubuntu, and then install Windows 7 on a virtual drive. It runs in a virtual environment on a virtual processor. You won't be able to run Windows updates, but you don't need them to run Windows. You can install Windows components that come as updates separately.
In my long experience with malware, I've never gotten them from security holes in Windows, of which I'm informed Windows 10 contains atleast as many as previous operating systems. Your best defense against malware is safe surfing and clicking habits and good anti-malware. Anti-malware that warns you of infected sites and won't let malware download or install works best for me.