I think you could have some value here, though i perfectly agree that you should be picking SelfConfidence.org, Confidence.org, Believeinyourself.org (i didn't like confidenceboost, may be confidencebooster could be cool) we all know its already taken.
I could also see that most of the extensions have been already taken for aplomb like
.xyz, .rocks, .website, .co, .me, .ca, .de, .tv, .co.uk, .net, .eu, .in etc..
Note: Aplomb.net is listed for $4000+ in afternic
A small suggestion my end is instead of developing it into blog (which requires good amount of effort) you could try reaching out to the aplomb.in who are into educational field. aplomb.org could make more sense to them if they are interested. Let us know how it goes, Good Luck.