I'm pretty sure I use a low-temp gun with multi temp glue (the glue for sure)
For flower ears, I haven't had any problems with flue softening unless I leave them in my car. The flowers are light enough that they don't pull the glue at all, so even if it does soften a bit, they aren't falling apart. I also wrap the wire around the headband and finish with glue/ribbon (to cover the underside) for extra stability.
I did have problems when I first started making ears when them falling apart in the heat, but those were with heavier embellishments (and hot glue really wasn't the appropriate glue for the materials)