Your setup looks good.
first you need to connect the blur node to your mix node and not the contrast/brightness.
Second use multiply instead of mix.
And tweaking the blur factor should give you the bloom you need. Maybe change the filter type from flat to gaussian. I get better results for glow effects that way.
no clue how the Glare node works,but that threshold looks promising…as in, glow everything above the threshold. have you tried just hooking your image up to the Glare node directly, and fiddling? Should be something in the release notes…
@Claas: best I could find in another thread for you is to either use the XNormal renderer which has a Glow shader, or to map it to an Emit material node(?), or I would think Blur it and use it as a Mix Multiply