Fragile, it is hard to translate it into Polish keeping all that conveys the original title. Literally it is: kwant pocieszenia. I've come up with "pierwiastek ukojenia", but there are surely better options.
I just checked "quantum of solace" against Google, and I found its meaning. Of course the ultimate translation would be difficult, as Thomas points out. However, I'm really fond of "pierwiastek ukojenia".
That is not the problem what any word means. The problem is, that it must be something difficult if that movie in Poland has no translated title. But I am sure, there is some answer.
What about the idiom: slabe pocieszenie? It does fit for your ears?
Some titles are simply better left in its original form, vide "Pulp Fiction". I think "Quantum of Solace" is on of them. I don't know what I'd think about this movie if it was titled "Słabe pocieszenie," which - answering your question - I don't think is an idiom.