Breakwire alarm (squib) utilising a transformer
I'd suggest you need to invert your architecture and get rid of the transformer altogether.
Perhaps something like this:







simulate this circuit &ndash; Schematic created using CircuitLab

With this you'd have 90 uA loop current and plenty of energy to fire the squib even with only a small 9 V battery. I've included both your 'safety' switch and a loop test switch so you know that the break loop is ok before you toggle the safety.