We use what I call a simmer mat. I get weird looks as though insane when asking for one at the kitchen shop. My Gran who predated electrics had one that was like a mesh mat impregnated with asbestos.
I use what most might call a metal trivet.
One version is just a pressed metal plate with bumps. The plate sits over the burner and the pot sits on the raised bumps creating an air gap. It spreads the heat from a small gas burner further while the air gap limits direct heating and boiling in the centre of the pot.
Another is two round perforated metal plates joined at the edges with a separation or gap of 6-8mm. It has a similar effect spreading and dispersing heat. The version I use has a wooden handle and looks a bit like a ping pong bat.
I suspect that the lower priced gas cooktops have less turndown compared to the Master Chef styled $5,000+ brands.
Maggie Beer in one of her recent repeats on SBS used a lidded casserole in an oven turned down to some very low temperature setting our oven does not possess. Apparently some ovens can be set low enough to ‘suvee’, although it’s advised not to rely on the oven setting and measure the temperature of the liquid directly.