The cheap stuff are generally going to be dubiously legit.
What’s your budget?
Home and Student is one of the cheapest options. Strictly not for business use, and one install only. Can be had for around £80.
I wouldn’t knock the 365 option. Price is about the same as Home and Student, but you get 5 installs, you get Publisher, Access and Outlook also unlike Home and Student, can install on Mac, iOS, Android, plus you get 1TB of OneDrive.
Downside is you have to pay up each year. Though monthly fee does spread the cost, and £8 a month is just a few cups of coffee. It’s a little cheaper on annual fee. Personally the fee alone is worth it for 1TB of online storage.
Oh, and yeah as above, check with employer as they might have a home use offer.