Is Avira (
https://www.avira.com/en/free-antivirus) still a good one? Along with AVG that is the one that I remember being a free option back in the day. I can't remember which one I used back then, the names are similar, but they are different products.
It appears that Sophos (
https://secure2.sophos.com/en-us/ products/free-tools) has a free home version now too. That was the anti-virus we had when I was at university, and at the time it did well on the "not very resource-intensive" front.
MalwareBytes is also a good option for free on-demand scanning if you've got something fishy going on, although they charge for their continuous real-time protection product. Still, a good supplemental option.
Norton, McAfee, and Kaspersky only offer free trials which expire after 30 days (and I'm not sure McAfee offers even that). Similarly with ESET, my general go-to for paid options.
Performance will vary by solution and the power of the computer you have. I have Norton currently, since it offered the best VPN-included deal and I wanted to be able to watch non-American Olympics coverage. When Civ4 was new, Norton was awful from a performance standpoint. Now, with my current laptop (a 2022 model), it's hardly noticeable. But on my 2011 desktop, there's a noticeable difference in responsiveness with it enabled versus disabled, whereas I don't remember ESET having a noticeable performance impact on the same system. Maybe now that the Olympics are over I should try Sophos's free version...
I recall you got a newer computer a year or so ago, so my guess is most options will have acceptable performance. But it sounds like there are at least four options to consider in addition to Windows Defender.