+1 vote for the differential probe.
It's not that expensive these days, Micsigs are around 200 USD. I think the person's safety is worth that much.
My method for maximum 500V AC measurement without Diff probe is that.
1. I use only one channel of the hand scope.
2. I insulate all the others with a rubber cap.
3. I only use a suitable probe, which was designed for this purpose.
Insulated BNC connection and the correct design for the measuring needle.
https://www.ebay.com/itm/134466286896?Thanks coromonadalix, I didn't know that the Ebay link was only needed up to the question mark. I'm always learning something new
4. The grounding of the BNC and the grounding of the calibration square signal and, if there is one, the grounding of the built-in AWG are connected! You also have to insulate them properly!