This morning, told my GF I’ve been looking at sectional sofas….

Your woman clearly knows how to get under your skin. This is common and probably nothing to worry about.

I have a Pi-hole and don't get ads.

There are LOTS of ways they can track you and it doesn't require listening to your phone. Not to say they never would, because they totally would if they had the chance but there are controls to prevent that for the most part.

For one you said that YOU did search for sectionals. If it was from the same device then for all intents and purposes she did too. Even if not, you probably both got online from your home wifi which comes out the same public ip addresses so they know you're all the same household. Then there's tracking cookies that can help identify the person looking at sites with the actual person. For example, if you're signed into Facebook on your phone and visit sites with Facebook tracking cookies and your wife is too then they can relate you two that way too. That's really just scratching the surface.

Using incognito/private browser sessions as much as possible and connect through VPNs are two easy and straightforward ways to mitigate such things to a moderate extent, but it doesn't sound like you're explicitly trying to prevent tracking, just wondering how theyre doing it.

Also this

LINK