What about trisodium citrate or Na3C6H5O7? The emulsion stabilizer that gave the world nacho cheese! Add it to any cheese and it’ll keep the fats from separating during melting, giving you a really smooth consistency!
Tip: reacting baking soda (sodium bicarbonate) with citrus juice (citric acid) will yeild a solution of sodium citrate of you don't have any/don't want to buy some just to try it out
Honestly I eyeball it haha. Juice a lemon/lime (or 1oz/15ml of juice) and add bicarb a little bit at a time until it stops fizzing. Make sure to stir it well before adding more
Yeah, this is crucial. Some of the cheeses under melting won't melt easily and will instead break under higher heats. Emulsifiers will prevent breaking and turn a lot of cheeses into melting cheeses.