MikeT, what do you use in preference to Windows?
Linux. This one: http://www.scientificlinux.org/
There are many versions (called "distributions" or "distros") of Linux. Mint is probably best for people who just want their PC to actually work, not spy on them, and get stuff done. https://www.linuxmint.com/
Ubuntu is another popular one. https://www.ubuntu.com/
You can try different distros until you find one you like. All at no charge.
Linux is free and will breathe new life into an ageing PC. You can dual-boot with your existing Windows if you want, choosing which OS to use when the PC starts. If you're happy with Linux, you can then delete Windows to reclaim the disk space. If not, try another distro or delete it. Your computer, your rules.
If you game, you are probably best sticking with Windows. That's all it's good for, a game launcher.
Windows 7 is ok privacy-wise, if carefully configured. I do use it. It's specifically Windows 10 I (and many others) have a problem with. Microsoft's business model changed dramatically with Windows 10 but they have kept this aspect of it quiet for obvious reasons. Office is now on a subscription (Office 365), and in time Windows 10 users will be forced onto the same pay-as-you-use model where you rent the software, rather than owning it outright. Credit card declined? No computer for you!
With versions of Windows prior to 10, YOU control and manage YOUR computer. With Windows 10, Microsoft controls and manages it and YOU are the product.
Anyone who thinks I paint my windows black and wear a tinfoil hat needs to do a little research.