Antivirus for Lion

You are between a Rock and a Hard Place.

Lion is not the best performing OS X release and adding an anti-virus package is going to make matters worse.

If you do install an A/V Package, suggest you see if you can configure it to do the absolute minimum and if you can tell it to NOT scan a lot of directories/folders it would cut down on the CPU and I/O resources it is going take on your system.

Lion is very old and increasingly insecure. Upgrade that to whatever is the most current macOS release supported by your Mac. That’s far enough back that it’ll be having increasing difficulties connecting to secure sites.

MacOS does have integrated anti-malware.

Alternatively, ask the company for a client system with a corporate-approved configuration. That’ll keep the company files and data off your own system.

It’s quite possible to dual-boot macOS, or to run various macOS versions in parallel as guests in a virtual machine. Which means you can still get at the old software, at least until the upgrade or the replacement is sorted out. Boot Camp (sometimes) or multiple partitions or an external disk are common approaches here. Details depend on how much free storage is available.

As for budgets, staying on old software versions and on old hardware csn save money at lesst in the short term— right up until it starts getting expensive. We’re all on an upgrade treadmill for software and for hardware, whether we like it or not. Particularly around security, but involving other areas and features as well. The treadmill won’t ever slow down, either.

Search Google for that information, reviews, etc. and ones that will work with Lion unless you can upgrade your computer to use a more recent version of OS X.