I’m desperate to write a nice melody as well.

I don’t tend to think in terms of scales but rather I think of chord tones because my brain just comprehends this way of thinking. Obviously you will most likely use scale tones but for some reason using scales makes my attempts sound like scales.

Personally, and I know it’s off topic, but I have been experimenting with using secondary dominants but I’m not sure how this would work within a DADGAD framework.